dispute resolution.
we cannot require the customer to file a police report.
we will give the customer credit.
but we would like to file a police report.
Can we require our customer fill out an affidavit of forgery so that we can use it to fill out a police report.

What kind of dispute, over what kind of transaction? Check(s)? Credit card? Debit card?

An affidavit of forgery would be useless and meaningless in connect with a card transaction. But if you're asking about a forged check, a further question comes to mind -- is the the drawer's signature that is allegedly forged, or an indorsement?

The Reg (E) and the EFTA are clear on what it takes for a consumer to file a claim. You can ask for whatever you need, but you can't make it a requirement to process the Reg E claim.