The how can be explained, the why however is more important.
You can do a spell and try to get her back, the love spell on the JOS website.
However you have to ask if she truly is the “one” for you. How did she affect you, positively or negatively.
If you truly were meant for each other, why did u split up?
Love is subjective and complicated, different for each person. These are questions you’ll have to answer for yourself after much contemplation.