Hello, @Jordi J.
When filing VAT returns, the VAT exception amount represents the transactions previously filed but was changed, deleted, or added. Once you enter an adjustment, it'll apply to the current VAT.
At this time, you have to reach out to our QuickBooks Online Support Team so they can assist you with the adjustments correctly. If needed, they also have specific tools to help you unfile the VAT return.
To contact support, tap on Contact us from the Help menu.
Also, check out these articles to learn more about VAT exceptions and reports in QuickBooks Online:
If you have any other questions, mention me in the comment section below. I'm always here to help. Keep safe, @Jordi J!
