First, make sure your site allow new user registration. Please go to your site admin > Settings > General. Here make sure you check to Anyone can register.
Now check this login & register documentation to know how to setup login and register pages.
Now go to your site admin > LearnPress > Settings > Pages.
Here you have to allow instructor registration and set the become a teacher page.
A user should log in and go to the become a teacher page to send a request for becoming a teacher.
Site admin will receive an email notification to allow or deny permissions.