In you Additio account, you can create the groups by importing them from Microsoft Teams.
You just need to access Evaluation and groups and right click on the + button, the option Import groups from Microsoft Teams will be displayed. You can also import groups from Microsoft teams on the three vertical dots > Import > Import from Microsoft Teams.
This is right the perfect time to link your Microsoft Teams account if you haven't done it yet.
Press on Link Microsoft Teams and it'll be automatically linked to the account opened in your browser. If not, you must log in with your user and password.
At this point, you are ready to import your groups. When you select Import groups from Microsoft Teams a list of your groups will be shown. You only have to click the correct group and the students of the given group will be listed. Now you can start with your assessment :)