Once in a great while I have this problem. What I usually do is too run a pipe cleaner into the airway, enough so that I know it has run down into the bowl. I then use my pick too lightly stir the ash itself and then lightly dump, removing the ash. Then I retamp what is left evening it in the bowl remove the pipe cleaner, relight and puff away. Sometimes If I've over packed I do the same thing, then with the pipe cleaner still in the airway I'll stir the baccy in the bowl using my pick, then lightly repack, remove the pipe cleaner, relight and puff away.