Create People in the system with the role 'League Administrator'
In the main menu from Admin Home:
People > List People > League Administrators
then press the button: 'Create new'
Enter their details, add the role 'League Administrator' to them. You also need to add an email address to them and check the box to send a 'login invite'.
Then press the button 'Create' - they will then receive an email from us with a link in it to create their own LeagueRepublic account and after doing so, they will be able to access the admin pages for your league as a 'League Administrator' and access everything you can.