run this codes
Sub fillIt()
Dim rs As DAO.Recordset, prevPN, curPN
Set rs = CurrentDb.OpenRecordset("710Convert_Claim_Listing")
Do Until rs.EOF
curPN = rs("POLICYNUMBER")
If Len(curPN & "") = 0 Then
rs.Edit
rs!POLICYNUMBER = prevPN
rs.Update
Else
prevPN = rs("POLICYNUMBER")
End If
rs.MoveNext
Loop
rs.Close
End Sub