There is clearly a way to make a new survey. There is no where it says to edit an existing survey. There is much Help on what and what not to edit, but nothing on how to edit. Specifically what menu (tab) to select and what topic from there that leads to editing the survey. I just want to delete two words and make the answer required.
There should be an icon that looks like a pencil (with the word EDIT) on the right side of your question. This is the link to open and edit your question – see graphic below:
Once you have opened the edit tab, you should be able to see the REQUIRE THIS QUESTION setting just above the question: