How do I edit a transaction in a closed year?

A client created the check deposit via "Add funds to this deposit" screen in QBO for correct payment amount of $5100 (check no. 1002) dated 5/15/20 (closed period)  that was supposed to be payment for invoice #1234. The emphasis is that this happens to be in a closed period.

a) I verified and check no.1002 has cleared back in 5/15/20 (closed period) for $5100.

b) also noticed a JE was posted in a closed period to record this $5100 check that (debits bank and credits services income) due to missing check at the time which client didn't record in first place since check found on 9/21/21. Doesn't this create a problem because it duplicates revenue/services, at least for the original invoice amount of $5000 and payment for $5000 matched against the invoice, aside from the $5100 check payment recorded via journal entry which is correct amount that cleared?

c) Invoice #1234 dated on 6/10/20 (closed period) was for incorrect due amount of $5000 and therefore received for incorrect payment on date of 3/1/21 (closed period) which are also uncleared transactions.

d) Since revenue (or services income I believe) is increased by the invoice from prior year 2020, then wouldn't adding the deposit as recorded by client in "Add funds to this deposit window" duplicate the revenue and/or services income again? 

e) This concludes that clients customer has overpaid since check for $5100 - $5000 = $100 in refund owed to the customer.

f) I attempted to create a credit on customers account via bank deposit in "Add funds to this deposit" screen.  (1st line item received from customer name, account has been changed from Services to Accounts Receivable, and Amount for $5100 and (2nd line item selected Account: Services and negative amount for -$5000) which I figured creates the $100 owed to customer. Instead, I am now seeing a credit of $5100.

g) Problem is I saved and closed the changes made, despite the alert I also got for it being in a closed period.  

h) Even if changing those amounts to come up with the $100 credit doesn't allow since QBO alerts that "you must specify a transaction amount that is 0 or greater. Is this because I am making changes in a closed period? Do these changes also affect my reconciliation for May 2020 when the check cleared? Please let me know if there are specific actions needed to correct these changes saved in closed period? Thanks.