You can manually add media to the media catalogue, or you can import media from a printer or from an XML file. However, you can always restore the default media catalogue. The existing media catalogue will be replaced with the default media catalogue. Any non-default media will no longer be available in the catalogue. If non-default media is used in your document, the media is not deleted from your document.
Click [Tools] - [Media] - [Media catalog].
The [Media Catalog] dialogue will appear.
Click [Restore].
Confirm that you want to replace the existing media catalogue with the default media catalogue.