You can import an Asset package in the Package Manager window:
Open the Package Manager window.
From the package scope drop-down menu, select My Assets.
The list view displays any Asset packages that you have purchased.
If a large number of Asset packages appear in the My Assets list, you can search for a specific Asset package by name or version number.
Click the Download button if it’s enabled. If you haven’t downloaded the Asset package to this computer or device before, the Import button is disabled, and you need to download the Asset package first.
While the Asset package downloads to your computer, a progress bar appears beside the Import button. A Cancel button replaces the Download button you clicked.
Once the download is finished, the Import button becomes enabled and the Download button becomes disabled.
Click the Import button to import the selected Asset package.
The Import Unity Package window displays all the items already selected in the package, ready to install.
Deselect any items you don’t want to import and click Import.
Unity puts the contents of the imported Asset package into the
Assets folder, so that you can access them from your Project window.