It's an easy fix. Is it the lume that fell out of the lume retainer, or the whole marker fell off (including the silver framing)? If just the lume fell out, you would need to decase the movement and glue the lume back in the retainer cup.
If the whole marker fell off, it may have a little foot that pokes through the dial and you apply glue to the backside (crazy glue, epoxy, whatever) where the post penetrates the dial.
ANY watch repair place should be able to do it on the cheap. Just go to a shopping mall repair guy or something...not an authorized dealer.