To help you remember your passcode (and protect you, of course), WhatsApp will periodically ask you to enter your passcode — by periodically, I mean once every 7 days and there is no option to disable this.
If you are still interested, all you have to do is:
- Open WhatsApp (Obviously!).
- Go to ‘Settings.’
- Go to ‘Account.’
- Look for ‘Two-step verification.’
- Tap on Enable.
- On the next screen, enter the six-digit passcode.
- Next, re-enter six-digit passcode.
- You can also add your email address on the next screen, but this is optional.