To set up an additional password to access the account from the web, do the following:
1. Open your profile and go to 'Settings';
2. Choose 'Security' -> 'Two-step login';
3. Tap on 'Use password' and enter your new password in the opened field;
4. Confirm your new password with an SMS code (OTP).
If you use the app, follow the steps from above and tap on ‘Set passcode’ instead. As an alternative, you would also be able to use Face ID or Touch ID on your iOS or Android device accordingly.