The app is available free of charge for iOS/iPadOS and Android. Installation is very simple. After loading the app, simply click on the 3 dashes at the top left. A new image will open.
Please select "My location" here.
Enter "Aachen" and then select "Aachen" on a gray background.
You will now be asked again whether you want to set the location to "Aachen". Confirm this with "Yes" and the app is ready for use.
Do you need more help? Simply select the "The app" icon (bottom right) and you will receive an introduction and further help - for example, how to call a contact address directly from the app.