how can i add extra frets on en xbox 360 xplorer guitar for solos? p.s i have a spare controller for the parts

the extra frets should press the fret and a strum

I'd chop the buttons, wiring, and the fretboard around the buttons from your extra controller. From this point, you need to cut a hole further up the neck of the project guitar that the new buttons will fit into snugly. You'll need to build supports for the new circuitry/button assembly into the neck, otherwise the whole thing will just bend inwards every time you play it.

From there, it's just a lot of wiring which I feel is best described here.

I wish you good luck.