Option Explicit

Sub test()

    Dim LastRow As Long
    Dim rngToSearch As Range, rngFound As Range
    Dim LookingValue As String

    'Create a with statement refer to the sheet that your data are store
    With ThisWorkbook.Worksheets("Sheet1")
        'Assigg to LookingValue the barcode scanned
        LookingValue = "1234"
        'Find the last row of column A
        LastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
        'Set the range to search for the barcode in
        Set rngToSearch = .Range("B2:B" & LastRow)
        'Set to rngFound the results from the find
        Set rngFound = rngToSearch.Find(LookingValue, LookIn:=xlValues)
        'If the result is nothing
        If rngFound Is Nothing Then
            'Message box
            MsgBox "Barcode was not found."
        'if you find a result
        Else
            'Add 1 to the existing value
            .Cells(rngFound.Row, 4).Value = 1 + .Cells(rngFound.Row, 4).Value
        End If

    End With

End Sub