Hello and welcome to the QuickBooks Community, kemmenes
We'll be happy to share some guidance on submitting VAT returns for your client in QuickBooks Online.
Accountants and bookkeepers can create an agent services account with HMRC for MTD services. This gateway can then be linked in QuickBooks Online Accountant (QBOA).
Once you have permission on your ASA to submit MTD on behalf of you client, direct your client to disconnect MTD in QuickBooks.
You'll only need to connect to your ASA Government Gateway once in QBOA (and then refresh the connection every 18 months). For each client that you are submitting for, you would then need to be added as an accountant user to their QuickBooks.
QuickBooks recognises the user-type that you're logged in as, meaning your client will no longer be able to submit themselves once MTD is connected to an ASA.
You can see more on QuickBooks Online Accountant here. We'll be around if you have any further queries!