Gently poke a blunt object like a hex key or an old brake cable through the stem to push the clog into the tire.
If you don't want to buy a commercial product, you can make a potent tire unblocker for ice at home using common household chemicals. tire unblocker
If your car has been booted by a private parking enforcement agency, there are several methods to release it without paying a fine: Gently poke a blunt object like a hex