In order to edit an attribute you need to place it in a dataview of the corresponding entity, you cannot edit an object into another object’s dataview.
Also for the sake of clarity in the forum I would ask that you don’t create a duplicate question, especially to your own. You can edit your initial question if needed or add a comment. Furthermore I will re-iterate on Wieke’s suggestion to look through the academy training, that should help you with the Mendix basics.
Hope this helps