Community settings>> Data Management>> Rebuild Data>> Rebuild Search Index
There are instances where ideas are edited, deleted or resubmitted in the community. This can make index less effective causing inaccuracy with search results. Rebuilding index will solve search related problems and speed up the search tool to get accurate search results.
Community administrator can rebuild search index from the above given path.
Time taken to rebuild depends on the number of ideas in your community. You will be notified that the operation is complete (via both the user interface and an email).