Was that in the Indexing Options, as shown here? https://devblogs.microsoft.com/windows-search-platform/configuration-and-settings/

If so, you can get there by going to the start menu and typing Indexing Options. Once there, clicking Modify would let you change what folders are indexed, and a Troubleshoot function. Clicking Advanced gives you access to a Rebuild option. If the files are in folders that are being indexed but there is something wrong with the index, that might fix it. But it might need quite a long time to finish the rebuild, like click-the-button-and-come-back-tomorrow long time. And if you are on a laptop, I don't think it does any indexing if you are running off the battery, so bear that in mind as well.