It works for me with modification, thank DCrack for sharing,
Private Sub Command1_Click()
Dim FldName As String
Set RsOld = CurrentDb.OpenRecordset("tabla")
Do Until RsOld.EOF
Set RsNew = CurrentDb.OpenRecordset("Select * From tablb Where tablb.manghiencu ='" & RsOld("manghiencu") & "'")...