If the print was dry mounted then the previous advice is probably the best. If like he says, and the bubble is still there then try the needle. Some dry mount tissue is supposed to be removeable after being heated again, but not all are.
I'm sure your safest bet it just to reheat it in the press. Sometimes when mounting a print at too low a heat or too little amount of time a bubble will be there. Leaving it in longer usually makes it go away.