Sometimes you may want to keep a signup to reuse in the future, but need to clear all the existing responses. Here's how:
Go to the appropriate hub and click on Signups. Find the signup you want to reuse and if you don't want new responses right now click on Close for Responding.
Then click on the trashcan at the end of the applicable signup. You will see three options.
If you want to delete the signup entirely click on the second option. However, you can keep the signup and only delete responses by clicking on the third option. You will get a warning, "I understand that this deletion is permanent and non-recoverable." Check the box and click on OK.
Your signup is still in the list but all existing responses have been removed. When a signup is closed for responding it is still visible in hub signups. If you do not want the signup to be visible at all, after clicking on Close for Responding you can then click on Archive.
When you're ready to reuse the signup you can Un-Archive it, Edit Signup Form if needed and Open for Responding.