Sanny wrote on https://superuser.com/questions/1075576/ms-word-for-mac-latest-version-resetting-normal-dotm
From this thread in Apple Exchange, the folder’s location has changed for Office for Mac 2016. It’s now located in
~/Library/Group Containers/UBF8T346G9.Office/User Content/Templates
For Office for Mac 2011 or if you upgraded from this edition to 2016, browse to this location
~/Library/Application Support/Microsoft/Office/User Templates/My Templates
In Windows, I can delete the file
normal.dotmto reset it. So you should try doing so in your Mac. You need first to close Word before deleting.