How can I set up a past VAT period?

​​​​​Hello, sakis.

I'd like to make sure I give the right steps for your concern. Do you mean to change the period on when you submit the VAT returns? If so, you can follow these steps:

1. Go to the Taxes > VAT.
2. Select the Edit VAT drop-down menu and choose Edit settings.
3. From the I submit VAT returns drop-down menu, select the period. 
4. Click Save once done.

To help manage your VAT return in QuickBooks, you can check out these articles:

• QuickBooks VAT return guide
• Manage VAT payments in QuickBooks Online
• Submit a MTD for VAT return to HMRC in QuickBooks Online

If you're referring to something else, please let me know in your reply. We're always available to assist you. Take care and stay safe.