What cream or moisturiser for his rash or ezcema not so sure what is this?

It looks like eczema. If it’s acne/rash, it will go away after a few days. If it’s eczema, it will linger and need to find out the trigger/cause. Do keep the area cool and clean and apply moisturiser for now. If need be, see a PD to get it diagnosed properly. Avoid steroid creams.