AEG competence fan rattle

The fan in the back of my oven has started rattling.

it is an AEG Competence B4140-1-m PNC 944 181 743

I have removed the protective ‘cover plate’ to expose the fan on the back wall of the oven.

I can see what the problem is – the fan does not have an equal gap between it and the rear oven wall, hence as it spins round it starts ‘knocking’ against the rear wall.

I can sort of remedy the problem; tightening up the bolt that is in the middle whilst holding the fan, problem is I don’t know if I am tightening or loosening as it doesn’t feel correct turning it either way. Now there seems to be a bit of ‘give’ on the bolt.

If someone could tell me the correct procedure to tighten the fan into place I would greatly appreciate it (or have I damaged the motor / fan assembly?)

Thanks in advance for any advice.