The subscription & free trial purchased on mobile device can be managed in the App store:
Go to settings - iTunes & App Store
Tap your Apple ID at the top of the screen
Tap View Apple ID. You might need to sign in or use Touch ID.
Tap the subscription that you want to manage.
Apple store reference page:
If you paid your subscription on our official website, you may go to your account page and manage the subscription.
The subscription & free trial purchased on mobile device can be managed in the Google play store:
Open the Google store play
Tap Menu - Account -Subscriptions
Find your VPNX subscription and tap on it
Manage your VPNX subscription
Google play store reference page: