WO events are edited from SFM Actions Menu if configured by your administrator.

Clicking a user event in Calendar or accessing it from the Recent Items page displays the event details using SFM View Event. Launch the Edit Event page from the Actions menu, if configured by your administrator.

To restrict the technician from editing any Salesforce event from the calendar, the admin can disable the check box against the Edit Events option from the General User Permissions section (Profile Setup> Manage Users> Profiles). Similarly, to restrict editing any ServiceMax events the admin can disable the check box against Edit permissions of ServiceMax Events from the Custom Object Permissions section (Profile Setup> Manage Users> Profiles).