You are on the right track using MP3tag to fix the tags and album art.
- Load the MP3 file into MP3tag and select it first by single clicking on the entry in the main window.
- Right click on the album art icon at the lower left of the window and select "Remove Cover".
- Add new album art by either right click again on the album art icon and select "Add Cover" to add a local image file
or
Use the Amazon.com album art option in the toolbar to locate the proper image online. - Clean up any other tags to fix album name, track number etc.
- Save File
- Enjoy