How to create selection dependant comboboxs and define data source

[tynawg]

Hello,
A forum contributer helped me create a dynamic array for 2 comboboxs which works great.
Now I would like to understand how to either create a third combobox or set of third comboboxs based on the selection in box 2?
Presently the first row of all columns is the title with the data below in each column the selection available to populate combobox 2. Once a selection is made in box 2 i want to have displayed a unit of measure, description of box 2 selection etc etc.
Below is the code to date,
If anyone can point me in the right direction it will be much appreciated.

Dim arr() As Variant
Private Sub ComboBox1_Change()
    Dim Index As Integer
    Index = Me.ComboBox1.ListIndex
     With Me.ComboBox2
      If Index = -1 Then .RowSource = "": Exit Sub
        .RowSource = arr(Index + 1)
    End With
End Sub


Private Sub UserForm_Initialize()
    Dim lastrow As Long, lastcolumn As Long
    Dim i As Long
    Dim ws As Worksheet
    
    Set ws = Worksheets("Sheet1")
    
    lastcolumn = ws.Cells(1, ws.Columns.Count).End(xlToLeft).Column
    ReDim arr(1 To lastcolumn)
        
    For i = 1 To lastcolumn
        lastrow = ws.Cells(ws.Rows.Count, i).End(xlUp).Row
        ws.Cells(1, i).Resize(lastrow).CreateNames Top:=True
        arr(i) = ws.Cells(1, i).Text
    Next i
        
    With Me.ComboBox1
        .RowSource = ""
        .List = arr
    End With
End Sub