Reset Canvas App to starting point

I followed the example for how to create a Messenger Canvas App, and I got it to work. The problem is that it creates a button. After pressing that button, it displays some text. I cannot figure out how to reset the program to go back to the button so that I can begin making and testing my own changes to the program. The only way I’ve been able to do it is to change browsers, but there are only so many of those. I’ve tried deleting cookies and the cache, changing the APIs, resetting the project. I’m getting desperate here.  The example code is completely changing what is on the canvas:

app.post("/submit", (request, response) => {
  const body = request.body;
  response.send({
    canvas: {
      content: {
        components: [
          { type: "text", text: "Someone just clicked something!", style: "header", align: "center" },
        ],
      },
    },
  });
});

I can’t try changing anything, because nothing happens at this point.