Valuation group code missing in Simulation -OMWB

Dear Sir

We want to purchase a raw material,for that I creating purchase order now,what is the configuration needs to automatic account assingment, where to create Valuation Group Code to assign to OMWD.

In OMWB,Simulation -> Purchase offsetting account-VlGCd is missing. where to assign it to group together.

Please help me.

Thanks

Rajakumar