When I try to edit my indoor rowing activities on the iOS Garmin Connect app, I can only enter the distance in metres (no kilometres), & only enter a distance up to 300m. Not that I wish to brag... but I (& I expect most people) tend to row further than that.
If you use a newer Concept2 rower, the ErgData mobile app will sync with the C2 logbook, which can be set to sync automatically to Garmin Connect by editing your profile and selecting Applications and then turning on synchronisation .