What am I supposed to enter in the Zoho CRM field in Forms?

What am I supposed to enter in the Zoho CRM field in Forms?

I thought that if I added the Zoho CRM field in Forms and tied it to a module in my CRM that it would allow me to do a look-up in CRM and fill that field.  Currently, when I use the form and I try to enter an account name, i get the error message "Select a choice for this field."  What does that mean?  What am I supposed to put in there.  

I would like for the for this form to update a record in CRM, not create a new one.