Updating the field

Hi,

I want to update the voucher Field In SalesTable , i placed a voucher field in SalesTable and make a relation vth CustTrans

but i want when i check the Markup Trans in CustOpenTrans Form then that related voucher Should only update in My Sales Table Form in (Voucher Field). i tired alot but their is only one common field between SalesTable and CustTrans i.e CustAccount and Voucher is comming from CustTrans Table.

so please suggest the answer for this solution.

Regards,

Santhoshi