On the default, this theme is for offline education and. If a user wants to enroll in the course, they have to fill and submit a Contact Form when they click on the button “Buy Course”.
You can choose the form you want your customers to fill in with the plugin Contact Form. You can use the form in Dashboard => Contact => Contact Forms. You can see in the below picture:
To apply a form to the “Buy Course” button, you need to choose it in the Dashboard => Appearance => Customize => LearnPress => Single Page, scroll to the “Select form Buy class”, then choose the form you want to apply, you can see in the below picture: