Mini-apps can be changed by republishing the app, to update it.
You are able to view the source code for your mini-app by navigating to the Files tab. You can make changes to this source code, remove the mini app and then republish it, but it is not possible to publish the changes at this time.
Adding an image to your mini-app tile
If you choose to add an image to your mini-app tile, this image should include the name of the app so that users know which app they are opening. The image file should be named "tile.png".