How to actually win a game as support

Im a bronze support main and didnt play to much ranked before. A few days ago I said to myself that i want to climb this season. There are just a few problems. The biggest problem is mid/endgame. In the early game I win 90% of lanes but I have no idea how to use that lead. Everytime it comes to midendI dont rlly know what to do now. Then i dont rlly know when to roam or which lane to roam I mostly just walk mid and cant get a kill there. So basically when minute 15 hits Im just walking around the rift like a child lost in maze.(Pls no comments saying”switch to a carry role” i know its hard to climb as a support but I wanna do it