I can't look at your photo on my phone but I have what I think is a tillermate. Its a sort of rope clamp that fits on the tiller. Turning the knob one way tightens the clamp and the other way loosens it. The rope is fixed either side of the cockpit.
If I'm talking about the wrong thing, please ignore.
PS I've bought a s/h tiller pilot so doubt if I'll be using the clamp thing.