To copy-pasteall values from one field to another, you will need to create a table view (if you don’t already have one) so you can see all entities, with the source and destination columns visible.
Then you need to select all the cells in the source column (and the only way is to manually highlight them using the mouse or shift+cursor keys), press Ctrl-C, then select the top cell in the destination column and press Ctrl-V.
(Ctrl → Cmd on Mac 
)