Hello,
we apologize for this Samsung specific issue. On Samsung devices we can’t open correct Settings screen.

Pls,

  1. Go to the Settings → General → Security → Apps with access to usage data
  2. Tap the “Avast Mobile Security” checkbox
    → “Allow access” pop-up is shown
  3. Tap “OK”
    → “Avast Mobile Security” checkbox is checked and you can go to the Avast Mobile Security app and set App Locking