If you mean the Library Lookup engines in the Zotero application (which comes with CrossRef and Google Scholar by default), you can download the engines.json file from here: https://github.com/bwiernik/zotero-tools
Then, place this file in your Zotero data directory, replacing the file that is already there.
You can edit the file to remove any engines you don't want before installing.
Then, place this file in your Zotero data directory, replacing the file that is already there.
You can edit the file to remove any engines you don't want before installing.