Hi,
if the shoes have laces, remove them. Relace leaving the bottom row of holes empty. This will give you more room. This is a wild shot, but try Smartwool RBX Racer socks. You could also try Superfeet cycling innersoles. It all depends on what is wrong, of course. if your foot volume is too large for the shoe, you need different shoes.There is a decent chance you need a larger shoe. If you are a little wide, then leaving a row or two unlaced might give enough extra room to help.
The Superfeet might help by supporting the rear half of the foot (which just might help circulation). Where does the numbness start? Is it near the cleats?