Hi :)
I presume that you must have customer Id or any unique identity of customer. Write a code like this on AfterUpdate event of you last name text box
Dim StrId, StrAddress,StrField1, StrField2 as String
StrId= =Nz(DLookUp("CustomerId","TblCustomers","CustFName= Forms!MyForm!TxtCustFName...