Hi, Nala83.
Allow to help and provide some information regarding VAT adjustment and reclaimable via QuickBooks Online Accountant.
You may want to make sure that you're using the correct VAT control account and you have reviewed all your VAT return before filing it through MTD. Once the return is submitted and accepted by HMRC, the option to correct it is currently unavailable.
Here are additional references that might be helpful for future use:
For account-related concerns, feel free to reach out to QuickBooks Support. You can get their updated number on this website: https://quickbooks.intuit.com/uk/contact/.
Should you have additional questions about VAT returns in QuickBooks, please let me know. I'll be around to help.