Once you've located the ES3 save file, open it in a hex editor. A hex editor allows you to view and edit the file's binary data.
If the file is not encrypted, it is stored as human-readable Locate the File : Most games store them in
If the file is (older ES3 versions or unencrypted):
Avoid editing "Quest" scripts unless you are following a specific guide. It can permanently break your playthrough.