Deploying a Kotlin Full-Stack Application on Heroku

I am a newcomer to full-stack development.

I chose Kotlin as my language to start because I was already familiar to it, and apparently Kotlin provided a wonderful tutorial on how to make a full-stack web app with itself.
However, I am very confused on how to deploy my application to Heroku, especially the part using database – because the app itself works, just not the database part.
So, I want some help on integrating the database used in the tutorial above and my Heroku application.
Thank you in advance.