At the end of each year teachers can archive classes created in Microsoft Teams. At the end of these instructions is further information about archiving a team with information from Microsoft.
To archive a team, follow the steps below:
1. Click on Teams
2. Click on "..."
3. Click on Manage teams
4. Use the search box to find the correct team.
5. Click on "..." next to the team you want to archive.
6. Click on Archive Team
7. Check the "Make the SharePoint site read-only for team members" box
8. Click on Archive.
To restore an archived team, repeat steps 1 - 3 and then:
1. Click on the "..." next to the archived team
2. Click on Restore team
At the end of the school year, it’s a good idea to archive the teams you’ve made for classes in Microsoft Teams as you prepare for next year’s classes. Archiving a team removes the team from your “Active Teams” list and freezes team activity. All content associated with the team will still be saved and you will be able to access it at any time. This includes files, conversations, grades, and assignments that you can re-use later.
Archiving does not delete a team. In an archived team, all activity in the team is frozen. This includes the ability to add or edit channels, post messages, or create new assignments. However, team owners can still add or remove team members and update roles. The team will no longer appear with your view of active teams.
The above was taken from https://support.office.com/en-us/article/archiving-classes-at-the-end-of-the-school-year-in-microsoft-teams-9d463caf-f98c-46a5-9318-fd37c5b2ff26