Within Teamwork, you can change the email address that you use for your account in your profile settings.
Click your profile icon in the top right and choose Edit My Details from the dropdown menu.
In the edit details modal, go to the Essentials tab to change the email address associated with your account. Click Update in the lower right to save your changes.
Updating another user's email address
If you are a site administrator, site owner, or have permission to manage people and companies, you can change the email addresses of other users.
Go to the People area of your site and select the People subsection.
Click the three dots to the right of the relevant user's name and select Edit Profile.
Alternatively, select the name of the user to open their profile view. You can then click the Edit button in the top right of their profile.
For more information, see: Adding Extra Email Addresses