The more direct approach if you're rooted: use App Manager, find your app, click the "X trackers" button in the header and if you still see adverts, look for any activities, services, receivers, that look like ads (usually highlighted).

For example (german):

There's also Warden, which can do the same but more simplified. They use both Exodus Privacy.

They both edit the app directly, without any background services or VPNs.