The best advise is quite simply… don’t touch it! Call a locksmith to extract the broken portion! Shoving instruments down inside to recover a broken fragment is almost never a good idea and will likely damage the cylinder. A locksmith will have the proper tools to extract the piece without causing harm. If by chance you do get the broken piece out or if it breaks on the outside, don’t loose it! It has the potential to save you hundreds of dollars! Take it to a locksmith to have them advise you on the best route to go. Most of the time they can simply cut a new one from the broken one and you will be on your way. If a code cut key is needed due to extreme wear, it is still far cheaper than having to pay a locksmith to come up with a new one from complete scratch.