I am new to pheromones and I want some suggestions. I am looking for a pheromone to help specifically win over this one girl I like even though she is in a relationship. I know that pheromones won’t make her like me, but it could make her be more open to me.
You should have posted this in the introduction forum 
Basically you are going to have a hard time trying to win her over if she is already taken. Do you know how long they have been together? Are things stable?
Have a read of this:
https://pheromonetalk.com/t/how-do-i-qualify-for-a-25-gift-certificate/19934
Then repost this in the Intro forum with a bit more info on yourself and your situation. That way you will earn the GC to help start trying stuff and we will have something to offer advice about.
Dude, respect the relationship. There are a lot of fish in the sea.
If there’s a girl you like who is not in a relationship, try AMMO and IH.
Dude I was in the same spot you were in a couple months back, there is this girl I met who’s a rep for a shipping company. About 5’7 average body type with the biggest natural boobs I’ve seen - no exaggeration double F cup!
But she’s been with this guy for 2 years 
Sure I wore my pheromones around her, even though she even said I was a “catch” and gave me respect and I couldn’t win her over because I drew a line and respected her relationship. (Personally I think I’m way better guy than her boyfriend - but oh well)
My advice: Keep in contact (don’t become her friend but flirt with her) and wait when they break up 
Then you make your move.