A damaged lock in your Honda Civic will make it very difficult to get in and out of the car. It's even worse if you feel someone else has got hold of your key, as your security is compromised. Either of these instances is a reason to change the door locks on your car. You need to replace the lock cylinders on both doors -- dual locks are readily available -- and you will now use a different key with the doors than with the ignition. The exact process may vary depending on the year of the Civic.
Roll the window all the way up. If the car has manual windows, disconnect the window crank from the door using a wire hook on its clip.
Remove both inner door handles -- the latch handle and the pull handle -- by prying out their small trim covers and removing the screws with a screwdriver. On doors with power windows, pry out the switch panel and disconnect its electrical connector.
Pry out the clips for the inner trim panel using a flat trim stick or similar panel removal tool. Lift the panel off the door. Pull off the water shield.
Detach the plastic clips connecting the outside handle to the latch and the lock cylinder to the latch. These clips are accessible through the door's access hole.
Remove the clip for the lock cylinder and remove it from the outside of the door.
Insert the replacement lock cylinder into the door and secure it with its clip.
Reattach the clips that connect the latch to the lock and the outer door handle.
Paste the water shield back on the door using its own adhesive. Reattach the inner trim panel with its clips.
Reattach the door handles and the trim panels. Reconnect the window crank if needed.
Repeat the process for the other door.