Where to add evidence for rent on my online portal

Hi all

I changed flats recently.

I just received this message but I rent from housing association so they confirmed my rent last time plus I dont see where to add any evidence?

Message: Your new housing costs cannot be paid because you have not provided sufficient evidence of how much you pay in rent. If you can provide this evidence, declare a 'Change of circumstances'. Housing costs will continue to be paid, based on your previous housing declaration.