hi @Joelle,
There is a guide on how to enrol with MTD here: Signing up for Making Tax Digital
Then once you have completed the enrolment there is a guide on making sure your settings are correct within quickfil here: HMRC Tax Accounts - MTD Returns
Have a go at working your way through those and this may resolve the issue.
Another way to check if you have successfully signed up to MTD is to log into your HMRC account, it should state on there (Rather than giving you the option to enrol).
Hope this helps