Hi, Does anyone know if a can cancel an open VAT return & start it again?

Hello there, candbbeautiful.

Thanks for checking in with us. I want to share 

The Open returns serves as the return based of the transactions. There isn't a way we can cancel an open VAT in QuickBooks Online (QBO). You can only edit or adjust the return as well as view the reports from the Prepare return drop-down.

You may want to check out this article to learn more about the whole process of submitting a VAT return in QuickBooks Online: Submit a VAT return in QuickBooks.

Should you need help or questions with something else, please don't hesitate to get back to me. It's always my pleasure to help.