I didn't mark your question a duplicate but it is already answered at https://travel.stackexchange.com/a/37005/4188 which points you at this resource describing how to use flight numbers with Hipmunk:
You’ll want to tell Hipmunk that you are flying out of LAX on Swiss Air 41 with a connection in Zurich. You’re then switching to Swiss 4324 for the final leg Istanbul (IST). We’ll write this ~~with double colons~~ after the airport code to signal that we have instructions for the search engine:
LAX LX41 ZRH LX4324
Double colons, as the post notes have been dropped since.
In your case:
