I purchased a domain name from a third party provider and parked it on 000webhost.com I would like to manually add an ssl certificate to my parked domain name. I looked and I regret to notice that there is no interface to enter the public keys and the private keys, in order to activate the certificate on the parked domain
You can certainly do this via Hostinger 
We have no SSL for custom domains on the free plan because the free learning plan is for learners to get up and running with web-hosting and make their website and get it online quick and easy
If you are at the stage where you are securing your website on a custom domain it sounds like you’ve made more than beginner progress and it is time to go premium to get all the benefits and features to progress further 