Hi,
I guess you have create a standalone app. When you click on Integrate >> Power Apps, you get 3 options =
1. Create an app => By using this, an app will be created with basic code/structure in it.
2. See all apps => This will get navigated to a page where-in you will see all apps created or shared by you
3. Customize form => By using this option, you can customize/edit your new/edit/display form in power apps.
I think you should select option no. 3
To see the customised forms, you will have to publish it and refresh you all items sharepoint list view.
