Add the online course calendar from your favorite studio to the home screen of your smartphone. This will allow you to open and use it like an app.
In iOS this currently only works with Safari.
Ask your favorite studio for the link to their booking tool.
Open the link to their booking tool through Safari.
Click the box with the arrow at the bottom of the menu bar in your browser.
Then select "Add to Home Screen".
Done - you can now access the booking tool directly from your home screen!