Join a specific team
Select Teams and then at the bottom of the teams list, select Join or create a team.
At the top right, type a specific team name in the search box and press Enter.
Find the team that you're looking for and select Join team.
You may immediately join a public team, but you must request to join a private team and then wait for the owner's approval to access the team and its channels.
Note: If a team owner hasn't enabled discoverability of their private team, you won't be able to find it by using search. You'll need to contact them directly to request to join.
Another option is to go to the command box at the top of Teams, then type /join to view a list of all your suggested teams. Choose a team to request permission to join.
Note: If user mailboxes are located on exchange on-prem, the Join or create a team area will not populate with public or suggested teams. The Join or create a team area will only show the Join or Create options.
Request to add a member
To add someone to a team that you're already a member of, go to the team in your team list then select More options > Add member.
Type the name of one or more people then select Send request. Team owners will receive an alert that they have a pending request.
First, tap Teams at the bottom of the app, then Join or create a team in the top right corner. From there, you can create a new team, browse existing teams to join, or join a team with a code (if you have one).