Hello there, @thesourcecoffees,
Currently, there isn't a way to change the option for MTD form from Prepare VAT return to Submit VAT Return. Please know that I'll take note of this, so our product engineers can consider it for future updates.
Using the bridging software requires you to have an active QuickBooks Online subscription. First, you'll have to authorise QuickBooks to interact with HMRC before submitting the return. Then, you can now perform the steps below on how to file the MTD form:
For detailed steps about this process, you can go through this article: Submit a VAT Return Through Bridging Software - MTD for Small Business.
If you're using the 2019 version, I recommend checking out these articles to learn more about our product enhancements, such as VAT e-filing and MTD:
I'm here anytime you have other concerns. Have a good day.