The Feature is not a Farm Level feature and is not found in site defined by - Could not enable Feature

All wsp's have a feature id. We could obtain the feature id of the deployed wsp using the following command.

get-SPFeature

Now search for the feature id of the wsp that you want to enable to a site.
This feature could be activated using the following command.

Enable-SPFeature -Identity FeatureId -URL SiteCollectionURL -Force -PassThru

Note:

FeatureId  Will be the feature id of the wsp 

SiteCollectionURL will be the url of the site in which the wsp has to be enabled.