I had the same question a few months ago, but had a ghost image whenever I used both eyes. Everyone one I talked to just said "train and it will go away", but no one told me how to train so the ghost image problem stayed and I just got frustrated. For the longest time, I just put a small piece of scotch tape over my left eye on my shooting glasses. This obscured my vision out of that eye just enough that the ghost image went away, but I could still see for reloads and still had my pariphrial vision.
However, a shooting instructor friend of mine recently sent me the explanation below. It really made sense to me and in the short little practice time that I have tried it the ghost image is becoming less noticeable. Hopefully, now that I know what I am supposed to be practicing I will be able to remove the tape on my glasses soon.