Convert to array functionality

[Dr. Demento]

The code below allows me to format a column based on the header value. Because my datasets are so large, performing this cell by cell is not feasible. Could someone assist in "converting" this code for use in an array?

I was going to change it to Function, passing the array I've already read in.

Thanks, y'all!

Sub FormatByHeader(Optional ByVal rngUsed As Range)
' ~~ This sub formats worksheet for SSN, dates, and rank

' ~~ Apply custom [number] format based on column header
' http://www.vbaexpress.com/forum/showthread.php?25740-Solved-Excel-2007-Apply-custom-number-format-based-on-column-header

Dim cell As Range, _
    cellx As Range, _
    rngX As Range, _
    row As Range
Dim strFormat As String, _
    strDtFormat As String, _
  
  Set wbk = ActiveWorkbook
  strDtFormat = "mm/dd/yyyy"

  With ActiveSheet
    .UsedRange  ' ~ Reset used range
    Set rngX = Range("A1:" & Cells(1, rngUsed.Columns.Count).address)  ' ~~ Set for range of header row | cells function gives the last cell in row 1
    [[COLOR="#0000FF"][B]substitute arrHeader for rngX[/B][/COLOR]]
    Set arrHeader = Application.Index(arr, 1, 0)   ' ~~ Define array Header || https://usefulgyaan.wordpress.com/2013/06/12/vba-trick-of-the-week-slicing-an-array-without-loop-application-index/

    
    For Each cell In rngX
      With cell
        Select Case True
        
        Case .value Like "SSN"
          For Each cellx In Intersect(cell.EntireColumn, rngUsed).Offset(1, 0).Resize(rngUsed.Rows.Count - 1)  ' ~~ confines column of corresponding header
            cellx = WorksheetFunction.Substitute(cellx, "-", vbNullString)  ' remove dashes
            
            If cellx = vbNullString Or cellx.value = "xxxxxxxxx" Then
              cellx.value = intPseudoSSN  ' ~~ assign pseudo SSN for any blank SSN
              cellx.NumberFormat = "@" ' Format as text -- REQUIRED!!
              cellx = Application.Text(cellx, "000000000")  ' format as text instead of number but retain leading zeros (DESIRED)
              intPseudoSSN = intPseudoSSN + 1
            Else
              cellx.NumberFormat = "@"
              If Len(cellx.value) <> 9 Then cellx.Interior.ColorIndex = 41  ' ~~ test if there SSN with more or less than 9 digits
              If IsLetter(cellx.value) = True Then cellx.font.Color = 26  ' ~~ test if there are letters in SSN column
              cellx = Application.Text(cellx, "000000000")
            End If
          Next cellx