It's impossible to take an MP4 file and convert it to the CD+G Karaoke format because there is no system that allows you to convert them. However, there are devices that allow you to load files from USB to play them. You could try that way. Look for the manual of the system you're using to see exactly what you can load into the machine/software.
You could also try the tools provided by the PowerKaraoke because they specialize in these things.