You can find all the Public Teams that you haven’t joined in Other Teams tab.
Tip：You can as well use the search box to search for the teams you want to join.
Following is the instruction on How to join a team.
1. Click Teams in the left menu.
2. Click Other Teams in the tab bar.
3. Follow one of the methods below to join the team you want:
Method 1: Click Join (word color: orange) to become the team member.
Method 2: Click the Team image to view the Team Subject and Description first. And click join the team button (button color: orange).
1. Tap Teams in the bottom bar.
2. Slide the tab bar left, and Tap Other Teams.
✎ Where’s the tab bar? The tab bar is right below the header. In the tab bar, you will see tabs like News Feed, My Teams etc.
3. Tap the team you want to join.
※ For the teams your have not join yet, you will see "not joined" under the team name.
4. Tap Join group.