I’m far from an expert with firmware, but I following firmware topics on the forum, and poke around in the source some. To start you need to know exactly what board you have. In looking at the firmware page for Mingda 3D printers, the only board that has a version of Marlin is MD-301. From a quick look, all other boards seemed to be using proprietary firmware, so If your board is not an MD-301, then you are probably SOL.
When I looked at the Marlin source provided for the MD-301, the source had been flattened and is two years old. In addition it does not appear that they folded their board back into the ongoing Marlin source. To me, this means you probably have some serious work tracing through the source in order to figure out how to integrate and/or update Marlin versions.
If you have a MD-301 then, if it were me, I’d start by installing PlatformIO and compiling and flashing their provided Marlin source. This would assure a functioning base version of Marlin as a starting point. After that, I’d use a difference tool like Meld to compare the configuration.h and configuration_adv.h files between the MD-301 version and a current V1 maintained version for the MPCNC.