You need to take that whole bottle into an authorized service dealer to have it inspected and serviced. They have special strap clamps to hold the cylinder and tools to remove the valve. They are most likely going to replace the whole valve assembly and the valves is not serviceable or available. This is due to the chances of catastrophic failure
Unless you are putting it in a place that you can't fit it with the tank attached then there is no reason to detach the cable. Just make sure that the valve on the tank is shut
