Hi John,
Welcome to the community!
Once you have received your confirmation email from HRMC you can turn on Making Tax Digital submissions in QuickBooks.
To do this, login to your account and go to Taxes and select 'Let's Go' . This will redirect you to HMRC to authorise QuickBooks to interact with HMRC using your MTD gateway details.
Once you have completed this you will be returned to the taxes page and will see the shiny new Making Tax Digital badge.