If you want to join someone’s team you will need the team icon:
If you have it, you can search by the team code. If you don’t have the icon, you'll have to wait for the Studio to roll out the feature to more players.
I would be interested in joining any team. My husband and I compete with one another. Being on a team seems to give him an edge.....that’s no good! My user ID is, 12242232094. I am currently on level 1965. I do appreciate your time and consideration.