The following operations are for use only in rare, specific situations and are not necessary during normal usage or for general troubleshooting. In many cases, resetting will cause additional problems. If you're not sure what these options do, please ask for help on the Zotero Forums before using them.
Before using any options on this page, make sure to first back up your Zotero library.
“Restore to Online Library” allows you to overwrite an online Zotero library with data from your local Zotero database. This can be useful if you've made unwanted changes to a Zotero library locally and those changes have already synced to the online library, or if changes were made on another computer and uploaded to the online library but those changes haven't yet been synced to your current computer.
Note that “Restore to Online Library” is only necessary when you want to undo changes already applied to the online library. It isn't necessary if you've simply made changes locally that you want to sync. For example, if the online library is empty and you add many items locally, those items will automatically be uploaded — the local items won't be deleted simply because they don't exist in the online library. Similarly, if you delete many items locally, those deletions will automatically be synced to the online library without your needing to take any special action.
Temporarily disable auto-sync in the Sync pane of the Zotero preferences, restore your local data from either an external backup you made or one of the automatic backups in the Zotero data directory, and then use “Restore to Online Library” to upload that version of your library. See Restoring Your Zotero Library from a Backup for specific instructions for your situation.
If the restore was successful, you can re-enable auto-sync. Keep a backup of your Zotero data directory until all applicable computers have had a chance to sync the restored version.
If changes made to attachment files are not being synced (e.g., edits, annotations, deleting an attachment, adding a new attachment), this option will reset the file syncing history between your local Zotero database and your storage service (either the Zotero servers or your WebDAV provider). This will cause Zotero to compare all attachment files on your local computer with the ones on your storage service, making the most recent changes to files.
Resetting file sync history should not be necessary, so if you find that files aren't syncing correctly, see Files Not Syncing for help troubleshooting and reporting the issue.