Master admins have the ability to change the master admin role to another self-serve within a company account. 
Please review this document before choosing the new master admin -
COMPLIANCE011 - Understanding the Role of a Master Admin  

Important - Company accounts cannot use groups or consumer domains. Instead, it must be the email of a single person who typically has financial sign-off for the company, and the domain must be your company domain.

1. Click Users on the left menu (if the new master admin is already a user, please delete their account first)

2. Profile menu on the left, select the "You (Master Admin)" tab.

3. Click "Edit" next to Login Email

4. Click "Edit." 

5.  Add their email address here and submit.  

6. New Master Admin will receive a code that you will key in here to validate.

7. Finally, once the new Master admin logs in, they need to update their "Profile" with their name, and their mobile number to receive their OTP codes via text/SMS.