Disappearing messages are automatically deleted after the selected time.

To activate disappearing messages in a chat:
  1. Open the chat.
  2. Tap the contact or group name.
  3. Tap on Settings.
  4. Select Disappearing Messages.
  5. Choose the time: 8 hours, 24 hours, 7 days, or 90 days and confirm.

Messages sent after activating this will automatically vanish after the set time.