How to add formula to a value format?

Question

Wishing to create an ID tag that auto indexes as data is saved from a form. The format of the ID follows the formula Left(B(cell),3). & "000"

I found code to index, but unable to shorten the B cell.

Dim sNm As String
Dim i As Integer
Dim nextemptycell As Range
Dim no As Integer
Dim AbcID As Range
Dim AbcNum As Integer
      
    'checking if sheet already exists in workbook
    Set wb = ActiveWorkbook

    sNm = cbocat 'selection in cbocat will be tested and or created.

    For Each Ws In wb.Worksheets
        If Ws.Name = sNm Then
            Worksheets(sNm).Activate
            MsgBox ("Existing sheet updated!")
            Set nextemptycell = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Offset(1)
            Do Until WorksheetFunction.CountA(nextemptycell.EntireRow) = 0
                Set nextemptycell = nextemptycell.Offset(1)
            Loop
                
        With Ws
            Set AbcID = .Cells(.Rows.Count, "A").End(xlUp)  'last used
        End With

        With AbcID
            If .Row > 1 Then AbcNum = Val(.Value)
                Set AbcID = .Offset(1)
            End With
            
            With AbcID
                .Value = AbcNum + 1
                .NumberFormat = """.Formula= .Left(b,3)""" & "-000"
            End With
               
            nextemptycell(1, 2).Value = cbocat.Value
            nextemptycell(1, 3).Value = cbosub.Value
            nextemptycell(1, 4).Value = cboreq.Value
            nextemptycell(1, 5).Value = cboclas.Value
        Exit Sub
    End If

What I see, with desired result in yellow

Output results from Edmundos' recommended code:

Answer 1

please try with this change, i just replaced the code where you are injecting the ID.

Dim sNm As String 
Dim i As Integer 
Dim nextemptycell As Range 
Dim no As Integer 
Dim AbcID As Range 
Dim AbcNum As Integer

'checking if sheet already exists in workbook
  Set wb = ActiveWorkbook

  sNm = cbocat 'selection in cbocat will be tested and or created.

  For Each Ws In wb.Worksheets
     If Ws.Name = sNm Then
       Worksheets(sNm).Activate
       MsgBox ("Existing sheet updated!")
       Set nextemptycell = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Offset(1)
         Do Until WorksheetFunction.CountA(nextemptycell.EntireRow) = 0
           Set nextemptycell = nextemptycell.Offset(1)
         Loop
        
       With Ws
          Set AbcID = .Cells(.Rows.Count, "A").End(xlUp)  'last used
       End With

        With AbcID
        If .Row > 1 Then AbcNum = Val(.Value)
            Set AbcID = .Offset(1)
        End With
    
        With AbcID
            ' * * * Change Here * * *
            .Value = Mid(.Offset(0, 1), 1, 3) & " - " & Format(AbcNum + 1, "000")
        End With
       
        nextemptycell(1, 2).Value = cbocat.Value
        nextemptycell(1, 3).Value = cbosub.Value
        nextemptycell(1, 4).Value = cboreq.Value
        nextemptycell(1, 5).Value = cboclas.Value
    Exit Sub
End If

Regards!