Fix the loose time set knob?

Electric Neff Circotherm oven Serial Number,
GB-1037,53LHSG or 195,304703 or 11800305. numbers from the plate inside the oven door.
I am able to send a photograph, if required

The knob which sets the time and also sets the start and end time for the auto cycle has come loose? Unable to engage the serrations. I am able to Isolate the oven from the Mains.

Can you please give guidance to tighten this knob to enable engaging the serrations.

Many thanks

Mike