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I'm sorry to hear about the updating gone wrong.
Is there no update for your courses? for instance, by having synced the device with a computer?
Think about whether the course files you formerly had on the device, were downloaded from copies on a computer, that you might still have.
I don't know how you performed the update, but, when dealing with an update for your Garmin device, it is best to simply download, install, and use Garmin Express.
and (if you have a Windows PC) click on the big blue Download button at center bottom of the page. (If you have an Apple, click on the nearby Download for Mac link.) And download Garmin Express' installer to your computer, save it, then double-click upon it to install Garmin Express.
Then start the program, Garmin Express. Then connect your Garmin device. Then use Garmin Express to update your devic