Step 1
Open Lightroom and select "File" from the menu. If the plug-in doesn't exists under "Plug-in Extras" select the "Plug-in Manager..."
Step 2
Once the Plug-in Manager loads, select "Add" to find the location of the Canon Print Studio Pro plug-in.
Step 3
The Canon Print Studio Pro plug-in should exist in the Lightroom folder. To find it go to "Applications→Adobe Lightroom Classic CC"→ CNPSPPILR.lrdevplugin" once the plug-in has been selected, hit "Add Plug-in" to complete adding it.
You should now be able to locate the plug-in under the "Plug-in Extras" tab in the File menu.