How to Archive a team
Pre-Requisite:
- You must be the owner of the team you are trying ot archive
Steps:
1. Open Up Microsoft Teams on your desktop or on the web
2. Select Teams 
on the left to see the list of your teams.
3. On the upper right hand side of the screen, you will see 3 dots. When you hover it, it should say More Channel Options. Click on that then select 
Manage Teams.
4. In the Active list, find the name of the team you want to archive, then select More options 
> Archive team.
Side Note; To prevent people from editing the content in the SharePoint site and Wiki tab associated with the team, select Make the SharePoint site read-only for team members (team owners will still be able to edit this content).
References: https://support.microsoft.com/en-us/office/archive-or-restore-a-team-in-microsoft-teams-dc161cfd-b328-440f-974b-5da5bd98b5a7