We would like a custom "Dead Lead" field in our Zoho CRM to be set to "on" automatically IF the value in an external spreadsheet is correct.

We used to do this before we switched to Zoho CRM using two excel spreadsheets--master and child.  On the master spreadsheet we used VLOOKUP to find a value on the child spreadsheet.  If the value was true, it would mark the lead on Master as a "Dead Lead".  When we switched the Master file to Zoho CRM, we lost that capability and don't know how to get it back.

Can someone help me understand where to look or how to do it? Do I need to upload the data to a zoho spreadsheet?