If you aim to move them soon, get the new hole/s ready to go, water the hole, dig up a large shovelful of soil with your dahlia and plunk it in the new location. Fill with soil and water again. They have a transplant additive you can put in the water- B 12 I think, but it's not necessary.

The plants will be less stressed if you make the move in the evening so they don't have to fight off heat and get further stressed til the next day, though I've done it on a really hot day and the dahlias will rebound in a week or so.