Thank you for joining the thread, @Hem.
I can help walk you through on how to record a VAT refund from HRMC in QuickBooks Online (QBO)
As the refund covers to a period not file within QuickBooks, you can create a deposit or record a journal entry to enter the transaction.
Every business is different particularly on the accounts used to handle each transaction. That said, I encourage contacting your accountant for additional help in identifying the correct posting account to use.
Just in case you need help with recording refund for future VAT returns filed within QuickBooks, check out this article.
Thank you for allowing me to help. As always, add a comment below if you have any other questions. I'll get back to you as quickly as possible. Keep safe!