As anyone who has used to Siri to make calls, search the web, or send messages knows, Siri doesn't always understand what you say. This can be followed by increasing frustration levels if Siri fails over and over to understand your voice corrections. But when Siri gets it wrong, you don't have to repeat yourself. Instead, you can edit your query via typing.
Swipe down to see your query text; then press tap to edit.
This will bring up a keyboard and allow you to edit your request by typing instead of voice. When you are finished typing, tap Done and Siri will respond to the corrected request.