You can look up uncrossing spells on the internet. Spells and rituals are merely ways to focus your mind and energy. Nothing is stronger than a spell that personally relates to you, which is why most people will tell you that it is best to write your own. But you can look up spells and rituals to give you a sense of what the nature of such spells include. If you find one that feels "right" there is nothing wrong with using it, but as I said, the best ones are self written.
The "power" is not in the spell but in you and how much you put into it. If you have never practiced before, I would suggest learning how to manipulate energy first. Magick isn't about ingredients, actions, and words. Those merely aid us. Spells and rituals construct an atmosphere that puts us in the right "mood" with the correct focus. It is an aid not a crutch.