Definitions for narrow down
pin down, peg down, nail down, narrow down, narrow, specify(verb)
"I cannot narrow down the rules for this game"
specialize, specialise, narrow, narrow down(verb)
become more focus on an area of activity or field of study
"She specializes in Near Eastern history"
Kernerman English Learner's Dictionary
narrow down(verb)ˈnær oʊ
to reduce the number of choices
I've narrowed it down to two wedding dresses.
Make more specific.