How do I update a vat return when I've input incorrectly?

Welcome and thanks for posting in the Community, @petermbaxter.

To update or adjust the VAT return to correct errors, please note that the following conditions should be met:

• The net value of the errors is £10,000 or less (reporting threshold). 
• The error amount is up to 1% of your box 6 figure (up to a maximum of £50,000).
• The accounting period ends not more than 4 years ago. 

You must report any errors that do not meet the above scenarios to HMRC. For more information, check out this link: Correct Errors.

Additionally, any manual adjustments will impact your VAT control or VAT suspense account. With this, I'd suggest consulting your accountant for further guidance on how to adjust the boxes on your next return.

Here are the steps on how:

1. Go to Taxes from the left menu to get to the VAT page.
2. Select Submit VAT for the period you are submitting.
3. Click Adjust in the VAT line that you want to change, then pick the Adjustment Date and VAT rate. 
4. Choose an account from the Adjustment Account drop-down list. 
5. Enter the adjustment amount in the Amount section. 
6. To describe the adjustment, enter a memo. 
7. Hit Save.

For more information about the process, consider checking out this article: Adjust your VAT liability. Once done, the system will automatically add a journal entry to show the adjustment. When you file your next return, this will include the adjustment.

I want to make sure everything is taken care of for you, so please let me know if you have any other issues or concerns. I'm always here to help. Have a good one!