Installing Thermostat for HVAC

We have a three McQuay PTAC HVAC wall units in our condo. One of them is controlled by an external digital thermostat, while the other two are controlled by the more basic internal controls, which consist of a red/blue button system and a dial to control the temparature. I’d like to install the digital control for these two units. I opened up the units to install the thermostate myself but it looks as though the digital thermostat was installed using a custom rewiring. Does anyone have any recommendations on an HVAC person who can install the digital thermostat for the other two units or thoughts on this?