How do I modify the settings in my custom app?

I am following the instructions in this tutorial for custom apps.

https://shopify.dev/docs/apps/checkout/custom/banners/add?framework=javascript

However, the banner implemented just defaults to the text that appears when there are no settings input, instead of the settings.current.description.

How do I set this? I do not see a field in my app settings.

Any help is much appreciated!