How do I add a new account admin?

Account admins

Settings

Account admins have administrative access to every program within a Message account, can invite new users at any permission level, and can manage the permissions of all existing users in the account.

After clicking the rotating gear at the top right of the platform, click Settings and then User Management. Click the Invite New Users dropdown, then select Account Admins. Type the email addresses for any new account admins (if inviting multiple admins, put one email at a time) and click Invite. 

You'll see all the Active Users on the User Management page, including their emails and their roles.

Once you input the email address, click Invite to generate an email invitation for the account admin to set their login information.