Edging height screw of my Conturo, not working properly.

[pinot]

I got a secondhand Conturo. It works perfectly, but it came with a problem. The last owner told me that some employee forced the knob to adjust the height  while the machine was cold  [mad]. The screw has a brass ring that connect it to the plate, that ring got loose.
I can use the knob to push the plate down, but to go up, i have to move the plate with my hand wile turning the knob.

¿There's some way to fix this?

thanks for your help!