Herein lies the problem unfortunately.
As kitchen fitters we fit our own appliances and do our own plumbing so bring all cables and hoses into cupboards, some don’t. If they were assuming the spark or plumber would take care of it before the worktops went on they’d not give it a second thought.
The dishwasher will unscrew from the cabinets. If it’s a Siemens, NEFF or Bosch there will be 2 brackets at the top and usually a secondary fixing through the machine into the cabinet 2/3 of the way down. You’ll also have to slacken the feet a little and drop the rear central leg.
Personally I’d get the kitchen fitter back if you’re at all unsure as they take a bit of lining back up afterwards.