If it is really important to get those badges you can try to delete activities and re-upload fit files to Garmin Connect, maybe the badges will be awarded again.
I don‘t care about badges, but I get "Treadmill 10 K or 5 K“ badge every run again since I delete treadmill activity created by FR935 to avoid double activities with Zwift.
If it doesn‘t work there is a second option - to repeat both marathons runs ;-)
