​@jsys14 - This is only possible if you do a “manual entry” to input the treadmill run on the web browser version of Strava.  Currently, you are not able to edit another entry like an automatically synced treadmill run or add elevation from the mobile app.  The only way is from the web browser and with an activity that you are entirely adding as a “manual entry”.  

Ok thanks for the information, I would like to suggest to add the option (i dont mind if only from the browser) to manually modify the elevation gain (EG) for an automatically synced treadmill run. In particular when I do a treadmill activity, the EG is not taken into account towards my annual goals. Also I would like to track the weekly EG i do, however it is not possible without this option.

Thank again,

That should be covered by the following feature request, you might want to vote for that: