How to create a vba code to run on the sheet to automatically remove all spaces in cells B3, B4 and B12?

Clarify 'remove spaces' please. Should 'This is a test' become 'Thisisatest'? Or leading spaces? Or fields contain no data but spaces?

Before
   This is a test   1

After
Thisisatest1

It works great, but it won't work unless I delete the existing macro already in that sheet.  How do I combine the two codes into one?

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim changed As Range, c As Range
    Dim cVal

    Const myR As String = "B5,B9" '<- Your range(s)
    
    Set changed = Intersect(Target, Range(myR))
    If Not changed Is Nothing Then
        Application.EnableEvents = False
        For Each c In changed
            cVal = c.Value
            Select Case True
                Case IsEmpty(cVal), IsNumeric(cVal), _
                        IsDate(cVal), IsError(cVal)
                    ' Do nothing
                Case Else
                    c.Value = UCase(cVal)
            End Select
        Next c
        Application.EnableEvents = True
    End If
End Sub

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I see you already asked this question somewhere else and got an answer. So you're all set.

Yes, thank you

Thanks!