Hello info194,

Thank you for posting here in the Community. I'm here to help provide information about the VAT return in QuickBooks.

Once a user marks a tax return as filed, you can no longer undo the tax filing on your end. You may need to contact QuickBooks Support for unfiling.

Before speaking to a support representative, please ready the required information. They'll be needing your QuickBooks Online Company and which tax filing period you wish to unfile.

To location the Company ID:

1. Click the Gear icon.
2. Click Account and Settings.
3. Go to Billing and Subscription.
4. Check the Company ID.

I'm also linking an article with additional information on unfiling a VAT return:
 

How to unfile VAT/GST.

In case you need the steps on how to contact support, please see the steps I'm adding below:

1. Log into your QuickBooks account.
2. Click the Help option in the upper-right corner.
3. Click Contact us.

Please reach out to me here should you need any further assistance with unfiling tax returns. I'm always available to talk QuickBooks.