well i guess all you would have to do it cut out the zipper, maybe just cut out the metal part and sew ribbon on top of where it was so it doesn't look all frayed or anything. then sew on some buttons where you want them in the fly. mark where they go on the top part of the fly, and then sew and cut some button holes! maybe try doing some button holes on a scrap piece of fabic if you don't know how to make them, they're a little bit tricky. (i'm talking about with a sewing machine, i'm gonna go ahead and think you have one
) so yeah. pretty simple! i don't know what these shorts look like but i always like shape and fun buttons.