Open WhatsApp
Tap the three dots or go to Settings
Tap Privacy
Tap App Lock or Fingerprint lock
Turn on Unlock with fingerprint or Face ID
Confirm your fingerprint, Face ID, or device passcode
Choose when WhatsApp should lock automatically
On iPhone, enable Require Face ID or Require Touch ID
On Android, enable Fingerprint lock
To lock chats, open the chat
Tap the contact or group name
Tap Chat lock
Turn on Chat lock
To lock WhatsApp Web, log out from linked devices when needed