Ours is a different model from that with no screws on the side of the main floor head, which is like this one: https://www.espares.co.uk/product/es1671457
It seems that you have to replace the complete floor head if the belt is damaged!

I googles "Air3 Pet disassembly"

Vax Air Pets and Family - Repair and A Look
https://www.youtube.com/watch?v=Q3b1SDo7PpA

--
Adrian C