It means that Mitsu wants to reprogram the memory chip in your
ECU.  They detected a problem at some point, and decided it was
serious enough to warrant a reprogram.

If it wasn't sent to you specifically, it may not apply to your
version of the EEPROM.

Some recalls are very specific to vehicles produced between
known manufacture dates.  In other words, they may have detected
the problem half way through the production year, and corrected
it.  Or it may appear only on vehicles with certain options.
That would leave only the first half of the years production, or
only specific vehicles unmodified.

Recalls are usually done by serial (VIN) numbers.

I did a google search, check out what others have said here;

It's a reflash to adjust the preheat timing of your cat.