How can I make my own universal prompt for bolt.diy?

I was searching the web but couldnt figure it out, can someone help?

There is no way in the UI to configure this yourself. You would need to edit/implement this on yourself.
The prompts can be found here: bolt.diy/app/lib/common at main · stackblitz-labs/bolt.diy · GitHub

But can I somehow include universalprompt.ts in the files and than so it shows in UI of the app?

You can do an additional prompt to the system prompt with a workaround within your project. See my video here:

Dont know if this is what you need. Another possibillity does not exist at the moment.