Stop Zoho Forms from Updating Zoho CRM if a field is already populated in Zoho CRM

Stop Zoho Forms from Updating Zoho CRM if a field is already populated in Zoho CRM

I capture data in Zoho forms and feed it into my CRM through the native integration. 

However, there are some fields that I would not like to be updated by the Form integration if there is already data in that field in the CRM. Is there a way to make the Zoho Form not write over data in an integrated field already existing in the CRM?