Factory reset is rarely the answer. Instead, try removing the app entirely from Connect IQ, restarting your watch (hold the button until it powers off), and then reinstalling the app.
Many users download a "Data Field" thinking it is an "App." Data fields cannot be run independently; they must be added to an existing activity (like Running or Cycling). how to unblock app on garmin watch
What if the app is a third-party download (like a crypto tracker or a specific golf course app)? Factory reset is rarely the answer