How do I use the app to stop a negative habit rather than create a positive one?

I have 2 suggestions (depending on the nature of the bad habit). 1. Try replacing the habit. Figure out what causes you to do the bad habit and replace it with a different task. For example, if you have a habit of leaving a mess after dinner, make it a habit to clean. 2. Try a different app. If you're trying to stop doing something that can't be easily replaced (like smoking), then you need a reward in the moment you skip the habit and a big reward at the end of the day. You'll have to decide if you want that reward in an app, internally, or externally.

Create a positive habit to replace the old one. I have struggled with trichotillomania with my eyelashes and eyebrows, now I make sure I plait my hair when I get the urge to pull or cut my fingernails 🙂