Migrating From HubSpot

Migrating From HubSpot

I am setting up ZOHO CRM and running into something I don't understand. I have multiple users is HubSpot and want to set up ZOHO CRM to recognize that certain contacts are already have assigned contact owners. I assumed I'd create a pick list and add the users to be able to have this field mapped before I migrate my data. ZOHO already has a field titled Contact Owner and won't allow my to add anything to it. Can someone please clarify if I am worrying about a problem that doesn't exist or provide me direction on how to proceed?  Thanks. JR