it's supposedly a method you can use to program a new (for example) MX 900 with legacy editor software. If you try to program a new MX 900 with legacy software without putting the remote into bootloader mode you will get an SC-1 error code and will not be able to go forward. I think you hold down Watch and Pause until the Loader appears on the panel. You should Google the proper keys. I may be mistaken.

In my experience, the bootloader mode does not work. URC even lists this as a method to try. Didn't work for me with 4 different remotes.

I was not even close on the buttons:

"1.Open up battery compartment & remove 1 battery from cup.
2.Press & hold the "On" & "Mute" buttons simultaneously. While pressing both buttons, reinsert the 4th battery into the cup. You should get a blue screen with the word "Loader" on the page heading.
3.Download your programming to the remote. If you get an eror message pertaining to the USB connection, ignore it, as your file should have down-loaded successfully. If not, run the boot loader procedure again."