to quote @jernandez:
"Changing a card's column is a nightmare
No way to do it from a card's view
Go back and drag it by hand
Run out of space with the trackpad for dragging the card horizontally
Half of the times it just doesn't drag it
The column you want to drag to is hidden so you have to drop the card somewhere in the middle, scroll, and continue your journey (failing and making the card's page dirty with fake column movements)"
Ideally: column is a field in an edit task with a pull down or autocomplete with the options of existing columns.