u can use "abzorb" powder for heat rash.. it works best. given by my ped

give body bath twice a day, and make baby wear cool comfortable clothes. after each feed clean baby's face with a clean, soft, moist cloth.. consult with paed.

my baby scratches his face where this rash occurs.

Nothing.  If it bothering the baby a lot then consult a paeditrician. As in if the baby is irritable. Breastfeed as much as possible. keep the baby in a comfortably ventilated room.