Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Your question is in the right forum. Close enough for me, anyway.
Silverlight is a web browser plug-in. You might find it in various places on your Mac. It's pretty easy to do a Spotlight Search to find Silverlight on your Mac.
The Sliverlight.plugin file is the actual plug-in. Put that file into the trash, empty the trash, and Silverlight is no longer available to run on your Mac. You may have a Silverlight installer and/or Silverlight Configuration Utility application somewhere on your Mac, which you can keep or trash. It's easy enough to download and install the plug-in again from Microsoft's Silverlight web site, should you change your mind and want Silverlight again.