how to update DFF field to customer site & site uses level using context sensitive DFF by bulk FBDI

how to update DFF field to customer site & site uses level using context sensitive DFF by bulk FBDI

we have to update DFF to customer account site & site uses level using bulk(19sheet) - we tried using below 2 sheets but not able to populate the DFF value to existing customers.

HZ_IMP_ACCTSITES_T & HZ_IMP_ACCTSITEUSES_T - but can see its not able to update the records, also what is the field name for context BU name which we also need to know for integration & migration to update the DFF value.

So we are looking for below 3 pointers related customer migration & integration.