It's not easy. But it can be done. Plugged cigars sometimes have a knot in the bunch that keeps enough smoke from reaching your mouth. A determined cigar smoker can attempt to massage the knot in order to try to loosen the bunch.
This is a delicate process. It takes some pressure to work through a knot, but applying too much force can easily split a cigar's wrapper. From our experience no matter how hard you try, you run a pretty good chance of splitting the wrapper.
Unfortunately, most draw problems stem from when a buncher has twisted the filler tobacco while making the bunch. If this is the case, massaging isn't going to help.
Some products have come to market allowing a smoker to punch holes through a cigar. We've had mixed results with these tools. In the long run, remember that cigars are handmade products and subject to the shortcomings of human beings. If you have a plugged cigar, perhaps you should simply chalk it up to experience and pick up a fresh smoke.