There is no way that you can fix it. You need to first check that you have the latest time zone map, which I'm sure you have by syncing via Garmin Express. If you have the latest map then you will need to contact Garmin Support and report the problem as they will need to issue an update to the Garmin Rime zone map.
Same issue here in California, 3 years later. We just changed to Daylight Savings time and my Garmin is an hour off. Fortunately Strava is smarter than my Garmin Edge 820, and my rides have the correct start time.
Maybe just on another point, my Garmin Edge 820 had a software update when I downloaded a training session onto Training Peaks and afterwards the time of day was totally wrong. I was using the unit indoors for the past 5 weeks because of the Covid 19 lockdown here in my country (South Africa). I could not manually set the time correctly.... until I read somewhere that if you take the unit outside and let it locate satellites then it will automatically determine your time zone and set the time correctly, and it actually worked!
Hope that will help someone with the same problem.
Had the issue for over 14 months now after moving from UK to US. Think i will have to bite the bullet and move platforms as Garmin seem to enjoy charging premium for equipment, then its back of a wagon support. Not sure why you cannot update your time manually, its been a standard option on most devices for over 2 decades, update time automatically or manual.
Had the issue for over 14 months now after moving from UK to US. Think i will have to bite the bullet and move platforms as Garmin seem to enjoy charging premium for equipment, then its back of a wagon support. Not sure why you cannot update your time manually, its been a standard option on most devices for over 2 decades, update time automatically or manual.