Unbounce to Amend a record rather than create a new one

Unbounce to Amend a record rather than create a new one

I am using Unbounce to create a form that captures a change in one of my fields in Zoho. But so far all I can do is create a new record in Zoho rather than amend my existing record.

I am sending the email address, the last name and first name from the form along with the data that has changed in the field.

If I make the email address in zoho unique I don't get the new field coming across.

If I don't make the email address unique I get a completely new zoho record.

Is it possible to amend a record from an unbounce form rather than create a new lead?