Running in reverse is just from the reverse switch being operated. Use the switch and it will just do it.
Running forwards needs the switch set to forwards AND a sensor switch that detects something is in the shredding path.
It might well be the sensor switch - usually a lever or tab in the intake throat - is broken. Possibly the shredder was reversed to clear a jam and has broken the lever.
You'll need to take it apart to see. I doubt spares will be available. You might be able to improvise. I did a while back for mine but it was only buying time.
Erogjh, February 2022
