Thanks for posting here, info-myalphavisi.
There are limitations when you import data to QuickBooks Online. Though we're unable to import previous VAT returns from Kashflow, you can generate reports.
Also, you'll want to have the PDF copies of the returns and upload them to Attachments. This serves as proof that you filed them already.
I've added these articles for more info:
Keep on posting here if you have more concerns. Wishing you all the best!