Payment Term not appearing in GGB0

Hi All,

we have the requirement if we post Credit memo in MIRO screen Payment term should be "00". Currently system is pulling what Payment term was there in Purchase order.

So I am trying to create validation in GGB0 if Document type is xx take the Payment term "00" but this Payment term is not available. Pl suggest how to make this available in GGB0 Tcode.

Regards,

Spandana.