Towards the end of the application, when you are back on the HealthSherpa website confirming the tax attestation, it will ask the client if they want to use the whole amount of their tax credit. Here you can opt to use the whole amount, a partial amount, or not use it at all. 

If you decide to use a partial amount or not use it at all, when your client completes their tax return, they will figure their credit and compare it to the amount of premium tax credit on Form 8962. If their actual allowable credit on their return is less than their premium tax credit, the difference, subject to certain repayment caps, will be subtracted from their refund or added to their balance due. If your actual allowable credit is more than your premium tax credit, the difference will be added to their refund or subtracted from your balance due.