This item is for use with the DeAgostini Millennium Falcon Cockpit photoetch set from ParaGrafix:
https://www.paragrafix.biz/product_detail.asp?PPartNum=PGX193
The ParaGrafix instructions call for the kit's rear wall to be modified quite extensively so that light can shine through and properly illuminate all of the exactingly designed buttons. This part does away with all of that work and simply drops into place.
Use super glue or expoxy cement to secure in place.