Yes, you can certainly reverse a journal entry in QuickBooks Online if you need to update it or make corrections.
Go to the Gear Icon ⚙️.
Select Chart of Accounts.
Locate the account used when creating the journal entry.
Click the View register from the Action column to open.
Find and click the transaction to Edit.
At the bottom of the transaction, click the Reverse option. A new entry is created with the original Entry no. followed by an R, dated the first day of the month following the original transaction, and the original transaction's Debit and Credit amounts reversed.
Once done, click Save and close.
That's it! Once reversed, all other information such as the Account, Name, and Description for each distribution line remains the same as the original transaction.