Remove A Bike Freewheel
Remove the rearwheel from the bike to gain access to the bike freewheel.
Replace the nut or the skewer to lock the key in place.
Use a long adjustable spanner to turn the key anti-clockwise.
If you have a bench vice you can clamp the key in it, drop the wheel gently onto the key then turn the wheel to unscrew the bike freewheel.