Update blank records to last record number + 1

[NicksMovement]

Hey all, I'd like to update blank records in a table to the next greatest value. The PONumber will be populated in a Form but the user will not have the option to update the job number. Eventually, I'd like to put a button on the form (or somewhere relevant) along the lines of "Update Job Numbers". I'm having a bit of trouble constructing the query that updates the blank cells as shown below. I'm not too versed yet in a lot of the SQL language or VBA so any insight here will likely be beneficial.

TestID	POnumber	Jobnumber
1	1856	1600
2	1857	1601
3	1858	1602
4	1859	1603
5	1860	1604
6	1861	1605
7	1862
8	1863
9	1864
10	1865

As in my last request, can someone point me in the right direction or direct me to a previous thread where this was solved? Thank you all for you time

[ranman256]

put code in a module then run it.

Public Sub IncrJob()
Dim rst
Dim sSql As String


sSql = "select * from table order by [Testid]"
Set rst = CurrentDb.OpenRecordset(sSql)
With rst
   While Not .EOF
        If Not IsNull(.Fields("jobNumber")) Then
            vJob = .Fields("jobNumber").value
        Else
            vJob = vJob + 1
            .Edit
              .Fields("jobNumber").value = vJob
            .Update
        End If
        
        .MoveNext
   Wend
End With
Set rst = Nothing
End Sub