im planning to use my gonna expired ebm for milkbath to treat baby's irritated dryskin and ezcema , anyone could teach me how to put for the ratio between water and ebm? and if ebm got to be heated up first before mixing together with warm water in the tub?

There's no perfect ratio. Some mums use only breastmilk whereas for me, I dilute it with water. Since your baby has ezcema, I recommend that you use more breastmilk as it is really moisturising and you can see the effect after a few baths. :) You don't even need to defrost or heat up the milk. Just pour it directly into the bath water.