If face recognition is no longer required, the registered face should also be removed from the Oppo smartphone, for which the unlock password is required.

Android 10 (ColorOS 7.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Fingerprint, face & password
Step 3:  Tap on  Face
Step 4:  Enter your current  Password/PIN/Pattern
Step 5:  Tap on  Face enrolled
Step 6:  Confirm with  Delete
  1. Open the Settings
  2. Tap on Fingerprint, face & password
  3. Tap on Face
  4. Enter your current Password/PIN/Pattern
  5. Tap on Face enrolled
  6. Confirm with Delete

Oppo Instructions