In case you want to install Comodo SSL, please check this article.
If you want to install your Lifetime SSL bought at Hostinger, check the following one.
If you bought an SSL Certificate from another provider, you can easily install it with us by following the steps below:
Open Hosting → Manage → SSL:
There click on Import SSL, choose the domain you want to install the certificate on, and insert values of the keys:
If you don’t see Import and Install options, most likely you already have an SSL certificate on that domain. To install a new certificate, uninstall the existing one first
If your SSL is still not valid after installation, please try to reinstall it. If it still doesn’t work, contact your SSL issuer
If you need help locating your SSL certificate's files and defining the type of file, please contact your SSL issuer's support