Mi start bottom does not work
So, how can I start the cycling activity
Which device?
If it is an Edge bike computer you can use the Edge remote and program the action button to start and stop the activity.
It is a GARMIN Vivoactive 3
Vivoactive 3 got auto activity start from Move IQ, but to enable that setting you need the button. It only works for walking and running.
https://www8.garmin.com/manuals/webhelp/vivoactive3/EN-US/GUID-A8048FBA-ABB9-4786-B888-303A20574D68.html
You can also try this: The Buttons on My Garmin Watch Do Not Respond When Pressed or Appear to Be Stuck | Garmin Customer Support