Hi there, will13.
First, you'll want to set up your VAT and enter your transactions. In this way, you can assign VAT codes along the process, so QuickBooks will recognise your taxes. This is what we encourage than entering your opening balances for VAT.
If you have many transactions, you can download them from your bank's website and upload them to the Banking page. Then, you can categorise, assign VAT codes and add them to your books. Once added, the information will flow to your VAT page. If there are returns that will show as unfiled though you've already filed them in actual, just mark them as filed. Once filed, you will see a Record Payment option on your filed returns.
Feel free to reach out again if you have other questions.