advice on leaking valve connection?

I hired a handyman to change out my kitchen faucet, lines and valves yesterday. After he left, I noticed that the dual output hot water valve is leaking at the connection to the 3/8" copper pipe that goes to the dishwasher. I think it's a compression connection.
Any advice on how to rectify this?
He is coming back to do some other work today, and I really, really need this fixed correctly (my dad has cancer and I need to leave town for several months).
Also, in order to reach the new valve connection, he had to pull some (about 3-4 inches) of the copper pipe out from behind the cabinet. I can't see what's on the other side (i.e.- the connection to the dishwasher, and whether it may have been stretched or compromised). Should I be concerned at all? I ran the dishwasher and so far did not see any leaking, so I hope the connection is still okay. How much extra pipe is usually coiled up behind the cabinets?
Thanks!

Leave the hot water to the kitchen sink/DW off until your handyman returns. The DW has a "kickplate" below that is secured with some screws (usually 4) that will allow you access to see under the DW. Shine a flashlight under there to check for leaks.

tubing

There is usually NO extra copper tubing behind the dishwasher, unless the original installer made a little longer turn than necessary, in which case your person could have "straightened" it out a little to get the extra length. But I do not know why he would have had to do that if all he was doing was replacing the valve.

Yeah, can we see some pics of the work in progress¿