How would I best treat this?

Hey, I'm clearing out my room, just found this at the back of my wardrobe (not been used in years), had loads of stuff in the way I've moved it all and wanted to know the best way to treat this? I've wetted it and put some mildew remover on it rubbed it with a cloth as my dad told me to do but as it's the only thing we have for mold in the house but I can buy stuff tomorrow when I'm out, anything particular you would recommend for this? I'm in the uk, thanks btw