This is currently not yet possible. I received this question quite a few times and hence I plan to include this feature in a future version of the app.
This app works completely offline. All data that is displayed on the map or used in the search dialog is bundled with the app. The amount of storage space available for that is extremely limited so that not all information that I would like to can be bundled with the app. Hence the data is restricted to countries and cities and it is not even possible to include all cities because there are too many of them on this planet. Especially the courses of rivers would take up a lot of storage space. A future version of this app might possibly include large lakes and mountains.
Developing and maintaining the apps takes considerable time. I intentionally avoid ads and rely on the users of my apps to pay a small amount for the apps themselves.
If you would like to support me financially, you can donate something. For a one-time donation, you can use any of the apps I have put online for that. There are apps for amounts of 1 Euro, 2 Euro, 5 Euro and 10 Euro.
If you would like to support my occupation with developing apps and other useful software on a regular basis, you can do that on Patreon. More information on that is available on my Patreon page.