Hi Blake - Welcome to Pherotalk. 
Well, yes there are various strategies for getting a GF back and yes, very many of them do depend on getting right out of her life and letting her find her way back to you, if she wants. There are a few good reasons behind this.
Not least because it gives you space to heal, look over yourself, your life and any personal issues that contributed to a breakup - More or less improve yourself in every way. And in the meantime, you may actually get a new perspective and to like your new position - after all, you now have many more options and this is where pheros can help.
Broadly, pheros fall into three main categories:
1 Sexual:
Ammo - Balanced sexy/social/attractive and for some, confidence boosting mix of the three main pheros, none, nol and rone.
TUTH - Very overtly sexual and really intended for those in an established sexual relationship. However it can be useful in highly sexually charged situations like parties and clubs with moderation from social pheros. Wear TUTH in the wrong environment and quite negative effects can happen. Use with care.
2 Socials:
Instant Shine - Happy/social/feelgood and confidence-boosting in all the good ways. About the most all-round phero there is and can be worn in most situations. Works very well alongside Ammo.
IO - Promotes flowing conversation and helps break the ice.
IH - Helps deepen conversation and promote bonding/trust. Useful when getting to know someone or to rekindle an old bond. 
3 Status:
IG - A light smooth/suave status formula that makes a good impression, esp in people around your age.
A314 - A blinder for work. Carries strong status/respect/trust/authority signals. Everything you need to get-on. Also useful in conveying strong LTR qualities but in socialising/dating it can appear too serious, standoffish or even dad-like, especially around younger women - don’t generally wear around party girls, use IG instead. However as they age, the A314 signal becomes much more attractive. Needs high congruence and time to get the full benefits out of it.
And in the meantime, it is probably better you move-on and get out there to have some fun and get to know other girls - for your own sake. You will become a more social and attractive person because of it and if you work with your ex, she will probably soon get to hear about it - which can also help.
Lastly, remember that as a 20yr old, you will probably have a reasonable natural none production and that girls around your age tend to be more responsive to lower/less overt doses of none rather than higher. So don’t underestimate the socials for their ability to trigger attraction - In fact they often work best with younger women. This changes as they age and of course, you can find exceptions at any age, so it is worth finding your sweet spot with several products so you can respond as the situation demands.
Have a read of this thread - All the basics on choosing and using pheros are covered: