You can never totally pull the dents out of a bubble.. there will always be a bit of dent or crease left, but this will help remove a majority of a dent.
First, you take your dented bubbled card. Next, you take a piece of DUCT TAPE, and roll it on itself (so it is a roll, but with the sticky side out.) Next, stick the roll of tape on the bubble. Hold the card so your hand is holding the edge of the bubble on the card. Then, pull the tape gently, hopefully pulling out the dent in the bubble.
Be careful as this technique, when done too hard or on a weak bubble, can pull the bubble off the card!