If a user has won a cash instant but hasn't claimed it yet, here's what you can do:
Firstly, export the instant wins in that particular competition and open it side by side to the CRM.
All the cash instants that haven't been claimed will say 'pending' in the sheet. You'll then need to tag all customers who are marked as pending (make sure to tag them all the same).
You'll then create an email stating they are a cash winner but haven't claimed their cash! (Make sure to link the button to the instant wins in my account).
Send out the email, but make sure to send it to the 'unclaimed' tag only.