If not your only hope of replacing a bad mcu and programming it is to know what the programming is that was on it.
First you would need to learn how to read/write the flash for this mcu. Not as hard as it sounds.
Then you need to find another unit with same model number either from a friend, purchase a working unit, or buy another "for parts" unit and hope its not the same issue. Then buy a replacement mcu and write the saved programming to it and install it back to your machine. Once you have two working units your good to sell one and keep the other if you need to recoup costs.