That answer was provided in response to a question about what the FBI is doing to investigate all the obvious shenanigans that Comey and Strzok were pulling with their sham investigation into the Clinton email scandal. When the Director of the FBI speculates in an open hearing that he might have to “unring that bell”, i.e., re-investigate the obviously false conclusion that the Pantsuit Princess did nothing wrong, it means he thinks there is a high likelihood that he will indeed be going down that road in the near future.