This will empty the File Index Queue. It will take care of only deleting the currently selected site's File Index Queue entries. You have to re-initialize the file index queue afterwards in the solr index queue module, or it will be filled from the record context or page context during indexing.
The file index queue is empty, you need to queue items from the storage context in the solr Index Queue Module, or enable the record or page context to index files during page and record indexing: