There is NO option for HTTPS on free subdomains from 000webhost.com
There is FREE HTTPS on 000webhostapp domains.
There is FREE HTTPS via CloudFlare and free domains from elsewhere like FreeNom.com
There is no sense in having HTTPS on a free subdomain from 000webhost - you will never own the free subdomain and it may be taken out of service at any time.
Just do not use HTTPS - use plain old HTTP.