Profile -> Settings -> at the top you will find the status of your subscription (here is an example of the Lifetime subscription).
Another way for iOS(if you have annual subscription): Settings of the Device > tap on your account > iTunes & App Store > tap your Apple ID at the top > View Apple ID -> Subscriptions > Select App in the Air from the list and there you can see when your subscription will end
You can check by using the following path: Choose an upcoming flight, tap on its "Flight Alerts" widget, then tap "Configure" (or "X More"). If flight alerts are available and you don’t see the screen prompting you to make a purchase, you’re on a premium.
Another way on Android: Go to our app -> Open Left menu -> Settings -> Scroll down a little bit and there you can find "Manage subscription"