It'll be in the user manual.
First Aid tips • Manuals • Cleaning & Care • Spaceports • and Accessories. Get convenient support for your kitchen appliances at NEFF!
www.neff-home.com
Grab a torch, open door, remove shelves, and look for it.
On my neff it's top right hand near the back.
Large bulbous glass cover, bayonet type fit. Very often hard to get off. Rubber gloves.
EDIT They look like this but have baked on grease so not that clean
https://www.partscentre.co.uk/neff-cooker-oven-lamp-assembly-12019100.html