If all you want to do is disable PAS, why not turn the ebike off using the display 's ON/OFF on the handlebar console? Does your bike also shut off when you squeeze the brake levers? You will see cables coming out of the levers if it does. If so, and if you just want to shut off PAS for low speed maneuvers, then lightly squeeze the brake pedals.
Connecting a throttle to a bike that doesn't have one is a different question. When posting pictures, it's easier if you orient the text so people don't have to turn the image sideways to read it. Your KT controller looks like it has two round cables in addition to the loose wire connectors.. Does one round cable go to the motor? Does the the other round cable go to the handlebar controls? When you removed the controller, did you unplug any of the plastic connectors, or were they always hanging free?
If the controller supports a throttle, there could be a three wire connector that was unused at the controller, but I think the throttle connection would be in the round cable that goes to the handlebars. What's on the other end of the round cable?