watch activity not syncing to my garmin connect app ios

You can try to repair the file using 3rd-party tools, such as FIT File Viewer. Runs in the browser and require no additional software. If you're still unable to import the activity into Garmin Connect, attach the file to this thread. We can take a look to see if it is repairable. 

• Zip the file, then in a reply post Insert >> Image/video/file >> click Upload >> browse for file >> OK.
• Or upload the fit file to a file sharing service, such as OneDrive, Google Drive, Dropbox, make the file public, then paste a link to the file in your post.