How to fix uneven eyes caused as an aftermath of a stye infection?

you have not posted photos, so it's very hard to know exactly what the asymmetry involves anatomically.  Without an exam, it will not be possible to fully evaluate you and give you recommendations. 

Without a photograph it is difficult to give a good answer. Typically a chalazia(stye) that drained on its own should not cause a Ptosis(droopy eyelid)of the eyelid but they can sometimes stretch the skin. I have seen a couple of patients that had styes drained by doctors where they went too high in the eyelid and accidentally cut the levator muscle causing a Ptosis of the eyelid.  You would need to be seen for a consultation to determine which condition you have but either one can repaired. 

Hard to say without pictures to help, but you may have an issue with the levator muscle that elevates the eyelid. Your upper lid should cross the upper iris revealing no white of the eye. If it is down close to the pupil, you will likely need to have the muscle repaired to fix this problem. Could be other things though. You should seek the advise of an oculoplastic surgeon.