I've never made rose hip syrup but I make all kinds of syrups in the summer and after looking at a few recipes this one is not much different.

You'll want to boil/simmer fresh hips in water until they turn into a pulp and then strain really, really well. The hips have hairs inside that are super irritating to the throat. So I would strain multiple times with a thick piece of cheese cloth or muslin. Once that's done you'll take sugar or honey and simmer that mixture until it thickens to the consistency you want.

It will be a while until I have fresh hips to work with! Rose petal syrup is really easy. You just steep the petals in water to make a tea and then add lemon juice and sugar and simmer until it thickens. Its quite lovely. It would be like this recipe but you need to use (3-4 cups) of water to make the juice.

https://www.walkerland.ca/strawberry-syrup/