I'll be amazed if a device like this has accessible UART pins, probably a blob chip.

If it DOES have UART chips you might be able to dump the binary and try and dig through it for what you are looking for.

Note, literally nothing about this would be a trivial job and it would likely be easier to create an entirely new PCB with your own MCU that fits in the same form factor and replace the whole control board. That still won't be easy, but probably easier.