Even I faced this problem to
update Garmin nuvi https://garminexpressupdater.com
for my adventure trip.
So You just have to connect Garmin Nuvi to your PC with a USB .
A window will pop up displaying the message new device detected as you have plugged the device.
• Look for the folder "Garmin"
•Discover the registry called "GPX", where your maps are stored.
Simply copy them onto your PC and open basemap ,which you can get from Garmin Basecamp download :
Then do anything like mark waypoints and tracks etc. from your computer.
Then add those tracked or marked maps in the garmin device.