How to export and edit a COROS FIT file

The COROS app can now crop the end of an outdoor activity, change its distance, and switch between a few related activity types. For anything else, like a section in the middle, the start of an activity, an indoor session, a heart rate spike, or a run that ended up in two files, edit the .fit file itself and upload the clean version.

What the COROS app already does

Check these first, because if one of them covers it, you don't need to touch the file:

Crop the end. Open the activity, tap the three dots in the top right corner, choose Crop, and drag back to where you actually stopped. Only the end of an outdoor activity can be cropped. The start can't, indoor activities can't, and some modes such as pool swims, multisport, and strength aren't supported. COROS says a crop can't be undone.
Edit the distance. Three dots, Edit, then the Distance field. Average pace adjusts to match.
Change the activity type. Three dots, Edit, Activity Type. Running, hiking, and walking can switch between each other, and cycling between road, mountain, gravel, and e-bike types. A run can't become a ride.

These change the activity in your COROS account. COROS's help doesn't say the change reaches Strava, Garmin Connect, or TrainingPeaks, so for those, or for anything else, use the file.

Step 1: export the file

From the COROS app:

Open the Activities tab (the second tab at the bottom) and tap the activity.
Tap the icon in the top right corner and choose Export Data.
Choose .FIT. COROS's own help suggests GPX only when heart rate doesn't matter, and FIT keeps everything.
Send the file to your computer by AirDrop or email, or open it straight from your phone's files.

From COROS Training Hub (t.coros.com): the Activity List has an Export Data option for your whole history. You choose .FIT or .TCX and COROS emails the files to you. This is the way to get many activities at once.

From Strava: open the activity on the Strava website, three-dot menu, Export Original. For a COROS activity that synced to Strava, that is usually the .fit the watch recorded.

Step 2: fix it

Open the file in FIT File Editor. The route is on the map, with pace, heart rate, cadence, power, and elevation on the timeline underneath.

A section in the middle. A wrong turn, a stretch on a bus, a long stop where the GPS drifted. Drag across it and press Cut. Distance, time, and averages are recalculated, and the gap becomes a pause. See crop a FIT file.
The start, or an indoor activity. The COROS app can't crop these. Drag across the part you don't want and press Cut the same way.
The watch died, or you stopped and started a new activity by mistake. Open the first file, press the plus button, and add the second. They join into one activity. The merge guide explains how the gap is handled.
Heart rate spikes. Optical sensors can lock onto your cadence, and a dry chest strap reads high at the start. Select the stretch and cap, smooth, or fill it with the fix tool. The heart rate spike guide covers which to pick.
Data from a second device. On a ride where a bike computer read the power meter and the COROS watch didn't, open the COROS file and add the bike computer's file. Power, cadence, heart rate, or GPS that the COROS file has none of is filled in from the second file over the time they overlap. What the COROS file already recorded stays as it was.
A sport the app won't switch. A run recorded in a bike mode, or an outdoor run that should be a treadmill run, can be set to any sport and sub-type in the details panel. See change the sport.
Wrong time. Shift the start time in the details panel with the time tool.

Press Export to save the edited .fit. The file stays in your browser the whole time.

Step 3: upload it

Delete the original activity on each platform first, then upload the edited file. Every major platform rejects a file that overlaps an activity it already has. The duplicate activity guide has the order for Strava and Garmin Connect.

Strava, Garmin Connect, TrainingPeaks: delete the copy COROS synced, then upload the edited file on the platform's website.
COROS: in the app, swipe left on the activity in the Activities list to delete it. Then sign in to COROS Training Hub on a computer, open Activity List, and choose Import Data to upload the edited file. The COROS app itself doesn't import files. COROS's help describes this import for files from other devices, so if it doesn't take your edited file, the original is still recoverable: deleted activities stay under All Activities, Recently Deleted for 30 days.

Worth knowing

Keep the original until the new one is in. The 30-day Recently Deleted list in the COROS app is your safety net. Strava and Garmin Connect have nothing like it, so keep the exported original on your computer.
Imports need a supported mode and size. COROS Training Hub takes .fit and .tcx files between 20 KB and 200 MB, in its supported activity modes. If an import fails, check the sport is one COROS supports.
Delete on every platform. Don't count on a deletion in one place carrying over to another. Remove the old activity on each platform where you want the edited version.