In Airstrip you currently can view your team, but cannot add or remove team members. To do this you first need to go to Dispatch, by clicking on the tool picker in the top left and selecting Dispatch:
Here you can go to your Team overview by clicking on "People" in the menu on the left.
You can view who's part of your team, add & remove people, and change people's roles in the team (except for the Owners).
You can add people by clicking on the "+ Add a team member" button. When you do so you can select the role they'll have in your team.
You can remove people by clicking on the dropdown icon next to someone's team role and selecting "Remove":
Changing someone's team role
You can change someone's team role by clicking on the dropdown icon and then selecting "Edit". There you can select the role you want to assign to your team member:
Note: People with the role of "Mentor" or "Stakeholder will NOT have access to the team's Airstrip project! If you want to give someone access to your team's Airstrip project you have to add them as "Team member".