Automated check-in enables you to check in and choose 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: left menu > Subscription

For an auto check-in request, on the "Boarding Pass" widget for your upcoming flight, tap "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.