How can we add pears or other library in PHP Capnel

Custom PHP modules and custom PEAR packages are not supported on free hosting, but you can add pure PHP modules with a system like Composer without any problems.

That said, I don’t see anything indicating missing modules in your screenshot. It looks more it says the XML-RPC API cannot be reached for “some reason” and I suspect that this reason is this:

https://infinityfree.net/support/javascript-error-using-api-or-mobile-android-app/