I'd second the recommendation for litespeed, not only that but Varnish is not supported by cPanel it is unsupported, and you'd find that we are limited in our ability to provide assistance with issues relating to 3rd party software that is unsupported.
If you really want to, install varnish you can change its listening port in the configuration, this is detailed in a number of tutorials for installing varnish on cPanel that are readily available with a google search.