Login to Namecheap or your domain registrar they are pretty similar with regards to the panels.
You can check your domain registrar FAQ section likely for a tutorial on how to URL forward.
Head to Domains then you’ll see all your available domains
Select your domain then hit Manage
You’ll need to revert to your registrar nameservers to use their forwarding feature.
Now you’ll see the option to forward your domain.
Type in your 000webhostapp URL into the destination box.
You can do the same redirection using the advanced tab also
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.
More information can be found here