How to I steal a popular girls best friend when I don't quite understand either of them?

I play soft ball on a team as a first year player. I'm in the last two weeks of 6th grade and I have been having problems with this girl and this girl happens to be the most popular girl in 6th grade. She has a best friend that is second up on the list of popularity. And they are both on my team I've been jealous of the 1st girl because she started a rumor that I stuff my bra and honestly I don't and yes I except that my whatever you would like to call thems are small but that's just the way they are and IDK but what annoys me is that people think it's true. Some people ask my BFF about it and she tells them non stop it's not true and I just ignore them and it works to keep them from bugging me and since it's not true I don't mind the rummer. But the girl is going to far so I've decided to steal her BFF so that I will be the firs girl and yes I have the power to do that but idk how to steal the first girls BFF when I don't understand them I am acquaintances with the second girl but the firs girl hates me. IF YOUR going to say that this is the wrong thing to do then ik that don't waist your time but if you have any help that will get either of them to like me other than being polite and friendly than lord please freaking tel meeeeeeeeeeeeee!!!!!!!!!