If you cannot get the Key Cylinder to turn (because of no key), then you may have to drill it out or replace complete unit:
Disconnect the negative battery cable.
Put the ignition switch in the Accessory (ACC) position.
Insert a wire into the small hole in the face of the lock cylinder. Push in on the wire to depress the plunger. Continue turning the key until the cylinder can be removed from the switch. .
Engage the electrical connector to the switch, then position the switch under the dash and install the switch bezel nut.
Install the lock cylinder to the switch. It most applications, the key should be installed and turned to the ACC, START or RUN positions in order to install the cylinder. If in doubt, check the switch or cylinder manufacturer's instructions, as applicable.
Once the cylinder is installed, turn the key back to the LOCK position.
Connect the negative battery cable, then verify proper switch and cylinder operation.