VBScript to Rename File with Specific Prefix in Folder - vbscript

Question

I have successfully created a VBScript that renames a file as required when it is the only file in the folder. I cannot figure out how to have the script search past the most recent file.
Option Explicit
Dim fso, folder, file, tmFile
Dim folderName
folderName = "\\pcc\Int\PC\Inbox\"
Set fso = CreateObject("Scripting.FileSystemObject")
Set folder = fso.GetFolder(folderName)
Set tmFile = Nothing
For each file In folder.Files
If (tmFile is Nothing) Then
Set tmFile = file
Exit For
End IF
Next
If InStr(tmfile.name, "TM") Then
TmFile.Name = Replace(tmFile.Name, ".txt", "A.txt")
End if
The above script correctly renames the file.
Here are a few modifications I have tried to go through all of the files in the folder to search for the file that has the prefix TM. This will always be the only file with the TM prefix.
For Each InStr(tmFile.name, "TM") Then
tmFile.Name = Replace(tmFile.Name, ".txt", "A.txt")
Exit for
and
If tmFile.fileexists(tmFile.name, "TM") Then
tmFile.Name = Replace(tmFile.Name, ".txt", "A.txt")
End if

Answer 1

You are close with your instr(), it's just that you need to put that test within your already existing For loop:
Option Explicit
Dim fso, folder, file, tmFile
Dim folderName
folderName = "\\pcc\Int\PC\Inbox\"
Set fso = CreateObject("Scripting.FileSystemObject")
Set folder = fso.GetFolder(folderName)
For each file In folder.Files
If instr(file, "TM") > 0 THEN
file.name = replace(file.name, ".txt", "A.txt")
End IF
Next
I've removed the tmfile variable since it's simply not needed here.