Merge

Tool to merge identical objects (sources, citations, repositories and media). Open the tool with the above command.

Tick the items you wish to merge. You can also choose if you want to merge citations that lacks content (only if extended citation options is used) and if you want to remove media not used.
  Note that no files are deleted.
  By default, the last option, Only citations without content is hidden and is displayed by selecting Use extended alternatives for citations in the settings.

See also