Extract part of variable in order to fetch user record in Zoho CRM

Extract part of variable in order to fetch user record in Zoho CRM

I'm trying to fetch a CRM user record us a fetched Zoho CRM custom user field. 

The variable ${fetchAccount_1.CUSTOMUSER} returns {"name":"John Doe","id":"12354656544564646"} 

The CRM user account does not recognize this. I would like to have the variable only return "John Doe"

I tried this but had no luck
${fetchAccount_1.CUSTOMUSERmapVar.get("name")}