@Shush1 

I would not suggest @LeizylM 's advice because you don't want to create a credit memo since you did not create a duplicate invoice or sales receipt, you just made an accidental deposit.  The easiest way to do this is to create an other current liability account called 'Due to Customer'.  Then, create a bank deposit and assign the newly-created 'Due to Customer' account under 'From Account'.  Then, write a check to the customer and assign the same 'Due to Customer' liability account as the expense account.  The only thing that is a bit messy about that is that you cannot combine it with other checks into a single deposit.  However, if you record them both on the same day, reconciliation is easy enough.  Undeposited funds (where you combine multiple payments into one deposit) can only be used on invoices and sales receipts and you have neither in this case.