Deploy a project to heroku again

I have a website that's running on Heroku that needs to be deployed again (because they deprecated Heroku-18 stack). I wrote the code, but an experienced programmer deployed it for me and I'd like to make sure it's deployed again and upgraded in a way that no data is lost and the project runs continuously and smoothly.

I think this would be an hour at most of work for an experienced Heroku user.