These are not very suitable for use with Let's Encrypt because Let's Encrypt is designed to be automated. These files are normally used with manual certificate issuance processes.
There are third-party web sites that let you request a Let's Encrypt certificate using these files, but you have to redo the whole process every time, before the certificate expires (that is, within 90 days). Let's Encrypt does not have any official site to do this because it's not a recommended way of using the service. It would be better if you could get your host to allow you to use the existing Let's Encrypt support inside cPanel, which would be easier and more automated. Normally the hosting provider doesn't have to do much work to do this—they just have to let you use existing functionality in cPanel!
If they don't want to do this, you might be interested in looking at