Pull File Names into Excel and replace dir

I am still a beginner with VB. With that stated, I am creating a vb script to help make part of my job a little easier but am havign a slight issue. I need pull all the file names from a directory (including subfolders) have them output in a column in Excel 2007. I get the first part to work GREAT, BUT my main issue is that when it outputs the list I need to replace "C:\" with "\\abcdefg123\" . I need just that part replaced with the rest of the file path following.

Sub FileNames()
    
    ListFilesInFolder "C:\<parent folder>\<subfolder>\<file>", True  
    
End Sub

Sub ListFilesInFolder(SourceFolderName As String, IncludeSubfolders As Boolean)

Dim FSO As Scripting.FileSystemObject
Dim SourceFolder As Scripting.Folder, SubFolder As Scripting.Folder
Dim FileItem As Scripting.File
Dim r As Long

    Set FSO = New Scripting.FileSystemObject
    Set SourceFolder = FSO.GetFolder(SourceFolderName)
    r = Range("A65536").End(xlUp).Row + 1
    
    For Each FileItem In SourceFolder.Files
        ' display file path
        Cells(r, 1).Formula = FileItem.Path
        r = r + 1 ' next row number
    Next FileItem
    If IncludeSubfolders Then
        For Each SubFolder In SourceFolder.SubFolders
            ListFilesInFolder SubFolder.Path, True
        Next SubFolder
        
    End If
    Columns("A:Z").AutoFit
    Set FileItem = Nothing
    Set SourceFolder = Nothing
    Set FSO = Nothing
    ActiveWorkbook.Saved = True
            
End Sub