Originally Posted by kiwidude
Go to your calibre configuration directory. Close calibre and then carefully edit the history.plist file. Inside there you will see the list of libraries from the history of usage of this combo, within the <asset> under the <key>lineedit_history_find_duplicates_plugin:libra ry_duplicate_combo</key> entry.
Thank you for pointing me towards a quick and easy solution.
I noticed my post was moved. Should all plugin questions/comments be posted in the appropriate existing thread, for example: "[GUI Plugin] Find Duplicates
" instead of in a new standalone thread? Glad to comply if it's preferred.