You can either edit/add/remove tags and locations for all sessions at once or you can add/remove them manually for each session.
You can add and remove tags and locations for sessions individually by clicking "Edit" button next to the session you want to edit. Scroll down to 'Location' and 'Tags' boxes and add new tags/location for the given session.
Alternatively, you can press "Tags and Locations" from the Schedule tab. There you can edit, add or delete tags and locations for all sessions at once by clicking "Edit" or Trash. You can also add new tags and locations so you can select them for future sessions.