Valuation type error

hi experts,

I want to change the valuation type for the material with existing stock. I have tried in Migo transfer posting with the 309 movement type ,but as soon as enter the material ,plant,storage location and batch the valuation type is picking automatically and it is in non editable mode.

kindly can anybody explain me how to change the valuation type of a material for the existing stock via MB1B or MIGO using the mvt 309?

I have tried in MB1B with 309 there i did not find any valuation type field?

Thanks and regards,

Bhargavi.