Originally Posted by dwanthny
It is time to upgrade to the newest version
of the plugin. If you believe you have upgraded then quit calibre - go to the plugins directory and rename the search_the_internet.json to search_the_internet.json.backup. Now start calibre and right click and choose customize. If all is working then delete the search_the_internet.json.backup file because it is no longer needed.
Many thanks, dwanthny !
I had an older version. Installed the new one and the "Customize" option is back. BTW, way better than before where, if I remember correct, you had to enter manually the search sites.
Kudos to kiwidude !