Venting integrated cookerhood

Hi

I have an intergrated cookerhood by AEG (HL 7275)
It is housed in a box built out of the wall (see pic)

Currently, it isnt vented properly, as there is no hose attached from the top of the cookerhood to the vent through the wall.(see pics). I gave a few questions on how to sort this out.

1)Is 100mm plastic flexible ducting ok to use?
2)How do I attach the ducting to the top of the hood? The instructions say that it comes with a coupling for this purpose, but whoever fitted it originally appears to not have bothered to do it properly. I've also had a look on the AEG website, but they don't stock spare parts for this model anymore.

Thanks in advance for any help!!

 

I know it would be better to not reduce the size, but the hole in the wall is only 100mm and I don't have the tools to make it bigger. Do you know where I could get a multiconnector that would fit the cooker hood opening?

 

Thanks, but what do I use to attach this to the opening on the cooker hood? As you can see in the 3rd picture, the opening is rectangular.

 

Thanks, I thought I might have been missing a part!! I had a look on the aeg website, but they no longer stock spare parts for that cooker hood. Where could I get this part, and what is it called?

 

Thanks for all your help! I think I will call/email the AEG product service, and see what they say before buying a new cooker hood