Login to GoDaddy.com or your domain registrar they are pretty similar.
You can check your domain registrar FAQ section likely for a tutorial on how to URL forward.
Head to My Domains then you’ll see all your available domains
Select the checkbox of your domain on the left then hit Forward
Type in your 000webhostapp URL into the destination box.
Some registrars will offer masking which means once it redirects to your 000webhostapp URL it will retain your custom domain by ways of masking it instead of displaying your 000webhostapp URL.
Either way is acceptable, leaving your 000webhostapp URL (Permanent 301) not (Forward with masking) will ensure the HTTPS/SSL lock is displayed.
Head back and you can even use subdomains this way.