You would need to go through your iTunes subscriptions page to cancel your PicCollage VIP membership.
- Go to Settings > [your name] > iTunes & App Store.
- Tap your Apple ID at the top of the screen, then tap View Apple ID. You might need to sign in with your Apple ID.
- Scroll to Subscriptions, then tap it.
- Tap the subscription that you want to manage. ...
- Use the options to manage your subscription.