Getting team admins to start using the mobile app for results entry is going to save your league money. In addition the team admins can also record stats for the match if that is something your league has setup.
To migrate over a team admin, all you will need is an email address for the team admin if there isn't already one in the system for them.
Follow these steps:
1/ Check Security
Setup > Settings > Roles > (Override button for Team Admins)
Make sure that they have security for
Enter results for teams within their domain
Enter statistics for teams within their domain
2/ Find the team admin and then give them a login.
Find them in
People > Search
People > List People> Team Admins
then edit them and if they don't already have their own sign in
CHECK - Send Login Invite
ENTER - Email address
3/ Team Admin will then receive an email - they need to follow the link and set up a login using a web browser
4/ Team Admin to download the app and sign in
Should be straightforward for them but full details are here https://help.leaguerepublic.com/live-results-team-admin-app-results-and-stats-entry/team-administrator-guides/how-to-use-the-team-admin-app
5/ Remove them from receiving the SMS prompts
Results > SMS > Teams > Click into them and DELETE