Hello @GregN4 ,
Unfortunately there isn’t a way to delete survey responses when it comes to the reporting of your survey. What you can do however is make a copy of that survey and when you send out the new copy those responses are reset back to zero.
The ability to edit the thank you screen within survey pages is listed as a feature request with us at the moment. I have added your name to this request to see customization for the thank you screen added to the product. Sorry for any inconvenience this may cause for you.