The repository conatins sample reports/app/and SQL code from my "Using Power Apps in Power BI reports: Enabling writeback" session and accompanying blog post here: https://shabnamwatson.wordpress.com/2020/02/21/using-power-apps-in-power-bi-reports:-enabling-writeback/
Once you open the Power BI reports, you must go to Edit Queries --> Data Source settings or follow the prompts if you click on Apply Changes to point the reports to your database. I used a copy of AdventureWorksDW sample database and added a simple Sales table. You can find the SQL code for that table in this repositoy as well. You can download the original version of AdvertureWorksDW here: https://docs.microsoft.com/en-us/sql/samples/adventureworks-install-configure?view=sql-server-ver15
Similarly you have to connect the sample Power App app to your database for it to start working. Go to Screen2 and click on the Connect url on the form and follow the instructions.
Finally you must save the Power App and publish it before you can use it in your Power BI reports.