If it's an elaborated trim and your piece has a "twin" trim that you can use to replicate the missing one, you can hot glue or silicon mold to make a mold and build a new trim with wood filler. Here is how I did it with this chest leg.
I'm not sure how big the area is, but I like to use epoxy wood filler. It doesn't expand or shrink, easy to work with, and dries quickly so you can sand/paint/stain.
Here a project that might help
If you post a picture that would help us help you.