We can’t help with individual accounting queries unfortunately, but someone like @FaradayKeynes (who is an accountant) may be able to help.
The best thing to do is to download a trial balance from the other system as of 31st March, and import this into QuickFile. This would set up all your opening balances for you. If you need help with this, please do let us know (and let us know what system you were using too), and we’ll try our best to help.
Other than that, this guide may be able to help with your opening balance query for VAT.