Currently, Tandem doesn't have a way for you to change the email address associated with your Tandem account.
The best workaround solution is to invite your new email address to your Tandem team.
From the main app, click on the + sign to the right of the team section and invite your updated email address to the team.
Because you will then have two of you in Tandem, you'll want to remove your older user. Admins can do this in the team settings by clicking on the three dots next to the user. If you are an admin, you'll want to make your new self an admin as well.
You'll then want to sign out of Tandem on your browser and the app.
Sign out of Tandem on your browser by clicking this link: https://tandem.chat/auth/signout
Click on the gear icon in the main app to sign out of the app.