I can't seem to find any pins on the bridge. Although I do believe it has something to do with those things below the bridge.
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You just have to push the string through the hole in the tailpiece until you can get a grip on the round metal thing attached to the end of the string, and pull on that until the string is all the way through the hole. Then feed the new string through the hole and pull it through the tailpiece until the metal thingy catches in the hole.