Head over to 1&1 and login with your email or domain or username.
Straight away you’ve got help to forward and the Manage Domain button
You’ll want to adjust destination
Then you’ll want to hit on Forward Domain
You can redirect using masking or without it.
If you mask sometimes this will cancel out the free SSL/HTTPS lock given by the free subdomain 000webhostapp.com.
For more information contact 1&1 here