If you are using Photoshop CC, there are a couple of steps to go through to ensure that the plugin is fully installed on your computer.
Once the add-on is acquired, click on the 'View My Add-ons' button:
Once on this page, you should see an Install button like this:
Make sure that you have the Adobe Creative Cloud program open on your computer, and Photoshop closed. Click on the Install button.
Upon clicking the button on the Adobe Exchange website, it can sometimes take a few minutes to install. Once installed, you should see this notification on your Desktop from Creative Cloud:
Open Photoshop and navigate to File->Scripts->KEY36.
If you are still experiencing difficulties acquiring the KEY36 plugin from the Adobe Exchange site, please go to www.36pix.com/KEY36 to download and install the plugin.