The contractor states that the dishwasher should have a power cord tro install instead of opening the back of the machine. Is there such a power cord?
If you go to the Bosch USA website and then check for your unit under Support/Owners Manuals install instructions are available (II).
It does show a special junction box/cord but also shows how to hard wire the unit.
Your unit does not come up on AppliancePartsPros.
It is probably too new to be on this site.
Give them a call if you decide to go the cord route as they have access to more info.