T code update VZGPO Loan management

Hello Guru,

My client using loan management and they changed their
address so they want to inform their client who has loan with them (contract)
about this so need a mailing list for based on contract and address related to each.

From before –before me_ they had a  Z report bit know when they start using it
just pick contract till one pint of tome not after that (almost) I talk to ABAP
and he said :

""    

For the given selection parameters, fetch loan
contract details from table VDARL

1. 2.
   for the entries obtained from table VDARL , go to table VZGPO and fetch the
   business partner details (type 'VD' for loans, role category '0100')

1. 3.
   for business partner details fetched above , get address details via function
   modules BPAR_R_ADDRESS_REFERENCES and BPAR_R_X_ADDRESS_REFERENCE.

I found certain contract no's are missing a business partner entry in table VZGPO
and getting skipped from the report output.

""

ABAP ask me what T code update VZGPO

So my q are:

What transaction updates VZGPO?

Would you please pass some of your guess why I donot pick all contracts?

Is there any other way that we can have this report?

Thanks for your help

Hamid