Do not worry if you can't fine the key for your expensive treadmill. You can still get it to work because the key is just a magnet that controls the console's power. Any magnet will work as long as it fits into the slot. You can purchase a magnet at a hardware store.
Locate the treadmill's keyhole. Most are located in the bottom center of the console for easy access.
Connect a small magnet into the keyhole.
Adjust the speed and incline to your specifications.
Press the stop button when you are finished.
Remove the magnet.