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.
Warnings
If the treadmill is under warranty and the magnet causes a malfunction, it will void the warranty.