Here's a link to the help center article on how to connect your Garmin.
https://support.grokker.com/hc/en-us/articles/360000423472-How-do-I-connect-my-Fitbit-Garmin-or-Google-Fit-account-with-Grokker

And here's an article on how Garmin works with Grokker
https://support.grokker.com/hc/en-us/articles/360000432211-What-activities-from-my-Fitbit-Garmin-or-Google-Fit-are-synced-with-Grokker