Singer Big Nine

Namely the pairs of white plastic hooked combs, which I believe were meant to do ribbing on the machine. I remember that one was used to pick up alternate stitches from the bed of the machine, – lift, then flip over and clip to it’s ‘pair’ resting on the front slot of the machine bed. But it isn’t quite that simple, I remember there was a ‘fiddly bit’ – which took me ages to grasp at the time, and which now completely escapes my memory. I would now like to get some use out of the machine, and try to get back into knitting generally, now that I have more time.
Can anyone help please? Does anyone have the instructions for using these rib combs?
Many thanks if you can help.