In case you are not sure which records have been duplicated, you can let CRM run a check on modules using the De-duplicate tool. CRM will automatically identify records with identical values in the selected de-duplication field(s) and merge them. In case of conflicts in field values, you must manually resolve the conflicts and merge records.
Consider the image below. There are two exact matches and there is one record in which only the Phone Number and Company fields differ. In this case, CRM will auto-merge the first two records and prompt the user to resolve the conflict in the last record. Once the conflict has been resolved, the records will be merged.
Since the lead's name is the same across these records, you might expect CRM to merge them automatically. However, CRM evaluates duplicates only based on the field(s) selected for the de-duplication check. Even if other fields contain the same values, CRM will not consider them unless they are included in the duplicate check criteria. In this example, CRM automatically merges the first two records because they contain identical values in the selected de-duplication field(s). The third record is not auto-merged because there is a conflict in the Phone Number and Company fields. CRM therefore prompts you to review and resolve the conflict before the records can be merged.
Availability
Permission Required
Users at the highest hierarchy in the organization or with administrative profile can access this feature.
This tool is available only in the Leads, Accounts, Contacts, Deals, Vendors, and custom modules.
What is a Master record?
CRM will automatically designate one record as the master record during the merge process. This record is chosen based on the latest Last Activity Time among the duplicate records. This occurs automatically and cannot be changed manually. For example, among five records, the record with the most recent Last Activity Time will be automatically selected as the master record.
Click the [Module] tab (e.g., Leads, Accounts, Contacts, and so on).
In the [Module] Home page, click Actions and select Deduplicate [Module].

In the Deduplicate [Module] page, click the fields by which you would like to search the duplicate records.
You can select up to three fields. CRM will search for duplicates based on these fields.
For example, if you select Email and Company, CRM will look for records in which the field values of Email and Company are the same.
Note that fields that you have marked as unique appear here. If you have not marked unique fields, CRM will display a standard set of unique fields for the module.
Click Find and Merge Duplicates.
A Deduplicate [Module] popup appears. Click Yes, proceed.

A popup window informing you of the de-duplicate function appears. Click OK.
If the records contain identical values in the selected de-duplication field(s) and no conflicts are detected, CRM will automatically merge them. In that case, no further action is required from the user. CRM evaluates only the selected de-duplication field(s) when identifying records for auto-merge. Matching values in other fields are not considered unless those fields were included in the duplicate check criteria.
Note that in the case of auto-merge, the record with the latest Last Activity Time will be considered the master record.
If there is a conflict between the duplicates in any of the field values, you must resolve the conflict and then manually merge the records.
Resolve conflicts in de-duplication
A conflict in de-duplication refers to a case where the field values within duplicates are different. For example, there are two records called David Smith, where all field values except the phone number are the same. In this case, CRM would not know which record to consider as the final and merge. Therefore, you need to manually resolve those issues. There are two ways to resolve conflict in de-duplication.
Resolve immediately - When CRM throws a popup on the conflict, you can immediately resolve it by click Resolve Now.
Resolve later - If you are busy with other activities, click Do it later. You will be sent an email notification on the de-duplication details. Access the link to resolve conflict from this email. Note that this link will be valid only for three days.
Once you click to resolve conflict, you will be taken to the Deduplicate [Module] page, where the particular record and the number of duplicate entries found are displayed. Click View.
(You can switch between the tabs to view the duplicates under each selected field.)
As per the example in the introduction, there are three leads with the same field values. So in the Deduplicate Leads page, you can see that the records are listed as columns.
Select a Master Record. You can click Select All, if you wish to take all the master record values as final and merge the duplicates.
If not, click the radio buttons near the corresponding fields of other records to instruct CRM on which field values should be considered "final".
The values thus selected appear under the Master Record column.
Once you have resolved the conflicting values, click Merge.
A warning message is displayed, informing you of the consequences of the merging of records. Once you are sure, confirm the action.
The duplicates will successfully be merged.
Notes
The De-duplication process can be initiated only by one user per module at a time.
You can merge a maximum of three records at a time.
If there are more than three duplicates, you will be prompted to choose any three to merge from the list of all duplicates.
Once the merge is completed, all related child records, such as emails, tasks, events, calls, notes, and other associated records, are moved to the master record.
The duplicate records are permanently deleted after the merge and the action cannot be undone. Only the master record remains available.
CRM does not maintain a report or audit view that lists the specific records merged through the de-duplication process. Once the duplicate records are merged and deleted, only the resulting master record remains available.
Read-Only fields will not have radio buttons.