Only a Team owner can add/remove members. Members can submit a request which will go to the owner for approval.
To add members to a team:
If you're a team owner, go to the team name in the teams list and click More options > Add member.
Start typing a name, distribution list, security group, or Microsoft 365 group to add to your team.
When you're done adding members, select Add. Fyi, you can make someone a team owner by selecting the down arrow next to the word Member. There can be multiple owners in a team.
Select Close. People you add to a team will receive an email letting them know they are now a member of your team and the team will show up in their teams list.
To remove members from a team: