From the Apple App Store or Google Play Store
App Setup
English, French (Canadian), Spanish, and German
Go to Settings, tap Account and Admins, and tap Invite Admin
Enter their name and email address
Tap Send Invite
Go to Settings and tap Account and Admins
Tap the Secondary Admin to view their profile
Swipe left over the name
Tap the trashcan to remove the existing user
Reach out to your service provider to request a Primary user change