Smart Timer and Counter is a jQuery plugin (as it is clearly stated on CodeCanyon, and WordPress is never mentioned). This is not a WordPress plugin and it can’t be installed in WordPress directly.
Depending how you want to use it, and where, you need to modify your theme (or a plugin where you want it), to load jQuery files, prepare HTML and JavaScript code to run it. Basically, all the examples in the plugin are for use it in the HTML project, what to load, how to init the code, and you need to take all that and custom code into theme or plugin to work.
I can’t really help with this integration, that is out of scope for the support of the jQuery item. If you are not sure how to integrate into WordPress, you need to hire a developer that can do that for you.
Milan