Well, I’m not sure if there is a way to make any search work like that. I can suggest a possible direct modification to the attachment search file, to allow only fully exact matches on the file name:
1. Make sure to have a full site back-up
2. Open up the .. file on your server
3. Replace it’s contents with this
4. Save the file
5. On the attachment search, I recommend this configuration: https://i.imgur.com/fxfhDlt.png
That should do only a completely exact field match on the file title. If you need help with the change, you can add temporary FTP details, and I will do it for you.