Here you can download and install the add-in directly from Microsoft AppSource: https://appsource.microsoft.com/en-us/product/office/WA104178141?tab=Overview
You can also get Pickit by going to the "Insert" tab in PowerPoint or Word, click on "Get add-ins" and search for Pickit. Click on "Add" and Pickit will get installed.
When the add-in has been installed successfully, you will find it in the ribbon under the "Home" tab in PowerPoint and Word.
In PowerPoint and Word 2016, you go you the "Insert" tab > "My add-ins" to find the Pickit add-in.