You haven't defined what myExt refers to and you have a counter 'i' which doesn't appear to be doing anything useful
myExt = Mid(Atmt.FileName, InStrRev(Atmt.FileName, Chr(46)))
Select Case myExt
Case ".xls", ".xlsx", ".csv"
will give you the required attachments.
You will have to save them as separate files before you can do anything with them. However it is not clear which workbook you want to import the files, but whichever it is you will not be able to do that until they are saved as separate files
Atmt.SaveAsFile FileName
'Import the saved file to Excel here
'
I think I would be inclined to make a sub that imports the current file into the workbook of choice and call it where indicated.