You don't reverse in this case, and if you have already closed the period there are ways to reopen the period and correct the error. However I would need a little more info from you.
If you are inquiring information with regards to your customer received payments the following would be Journalized:
In this case, there are three accounts affected. When a sale is accomplished there is an increase to Sales, Accounts Receivable and Revenue this is why you are seeing an increase in your Revenue. You would do a Journal Entry since these accounts originally were increased at time of sale, you would do the opposite to the Income Revenue. With that being said you would do a Journal Entry, Debit to decrease the earnings, and the AR (Customer) would also be decreased with a Credit, originally the AR was Debited with an increase.
If your true question is with regards to an expense, (Your company spent the money) you would do a Journal Entry to decrease as mentioned above to the Income Revenue and you would journalize with a Credit to your expense (Name of Expense). All normal balances with Expenses are a Debit which increases your expenses, when you want to decrease an Expense you do the opposite with a Credit.
I always review all situations before I begin making any type of changes to the accounting cycle in the event you make a mistake the results become a Domino affect and creates additional understatements in your Income Statement. Thus you would want to consult with your accountant or if you need additional help please feel free to advise me I am an Accountant.
Kind Regards
ML
