If you get confused with wish...

As I said, wishes are unreal. However, if this confuses you, just go back to our unreal conditions.

For example:

PRESENT:
I'm not in Hawaii right now, but if I were (in Hawaii right now), I'd be drinking a margarita with a pretty little umbrella in it.
I wish [that] I were in Hawaii right now. (Imagination/unreal)
Unfortunately, I'm still in Houston. (Reality)

PAST:
I didn't know that you needed help yesterday, but if I had known that, I certainly would have helped you.
I wish [that] I had known [that] you needed my help yesterday. (Imagination/unreal)
Unfortunately,  I didn't. (Reality)