Automated check-in enables you to check-in and chooses your favorite zone prior to the airline check-in window opening. Thus, you don't have to worry about the availability of your preferred seat! This is a part of the premium subscription, but you can try it free for 14 days (access the free-trial period is in the annual subscription). 

For iOS Go to Profile > Try subscription; For Android: Profile > Settings > Manage subscription

For an auto check-in request, on the "Boarding Pass" widget for your upcoming flight, tap "Auto check-in", then go through the steps to fill in the necessary information, and then tap "Submit".

If you want to add passengers for auto check-in, tap the "+" button before hitting "Submit", fill in their information and preferences, then submit the request.