Open an existing Teams chat, or start a new one.

If you are starting a new chat, type in the email address of the external user you are chatting with, as well as the email of any internal WFAA staff.

If you are adding the user to an existing chat, tap the View and add participants button in the top right corner of the chat.

Type in the external user's email, then choose whether or not to share chat history with them.

Select Add.