After installing Redmine, you need to do some initial configuration. When I looked for helpful sites, I found that the official site had clear documentation, so reading this should be sufficient.

・Redmineを使い始めるための初期設定 | Redmine.JP

Also, for those considering installing Redmine on Heroku, check out this article:

・Heroku に Redmine を設置する手順 | CodeNote.net

That’s all from the Gemba.