Description field for billing plan date items

Dear all,

I have to add a free description field for billing plan date ítems in VA01/VA02. In table FPLT I have founded field DESCR Billing Plan Item Description which meets the requirements but I haven't been able to find any billing plan screen or interface where this field can be updated. Does anyone know how and from can this field be updated? Which are the available options to include this field in VA01/VA02?

Thanks in advance.

Ibai Revilla