Activities in the calendar can be edited (in certain ways) by members of the Unit Council, or by the activity organiser. Adult Leaders should form part of your Unit Council.
If you’re still not able to edit an activity, make sure in the Unit view in the member area of Scouts | Terrain that you are assigned to a Unit & form part of the Unit Council.
In the near future we are working to improve the edit possibilities for activities, including being able to edit the date, time and title of an activity.
If you need further help, reach out for support from the support page.