First buy a new port cover, i bought the whole package at witrigs.com a while back after the rubber ring was broken.
Second, take a paper clip and flatten it with a hammer, see pic.
Then stick the paper clip in, along the side where there is a kind of barb. Do this carefully till you reach the point where you can't push it further.
After you pushed the paperclip in pull the cover out by pulling on the cover and at the same time loosen the paper clip.
I hope this helps.