We covered how students join a teacher's library. This article looks at how, as a teacher, you can join another teacher's library. This is particularly useful if they want to add you to be a co-teacher of their library. You need to join their library before they can promote you to co-teacher.
You'll need the library invite code first, which your colleague can find and then send to you (there's no automatic way of sending it, they'll need to email or message you the code, or show you in person).
Use the menu icon in the top left to access the Teacher Dashboard. Scroll down to the Shared with me section to find the button that says Join a library. Click on that and then manually enter the invite code.