You cannot turn off Stolen Device Protection without Face ID if it is required on your iPhone
Use Face ID to authenticate, then go to Settings
Tap Face ID & Passcode
Enter your passcode
Tap Stolen Device Protection
Turn Stolen Device Protection off
If Face ID is not working, set up Face ID again first
If Face ID cannot be used, wait for the security delay and try again in a familiar location
If you still cannot access it, contact Apple Support