Accelerator cable stuck wide open

How can I unstick my accelerator cable. The van has been off the road for a month as I can't free the accelerator cable. Can someone give me some info on the proper way to do this.

Thanks

What year? What engine? Is the return spring missing or broken? Does the cable have a kink? If you disconnect one of the ends, does the cable move freely? Do the parts the cable is connected to move freely when the cable is disconnected?