Probably in your device after the upgrade the gupdate.gcd is deleted automatically.
backup your unit content before doing anything
1. Connect unit to computer and open my computer
2. Open Garmin drive then the Garmin folder
3. Open the Remote SW folder and delete the contents
4. Copy the old fw file gupdate.GCD in root directory.
5 Power circle

zumo 550 fw 4.80 GUPDATE.rar (2,8 MB)
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