Do you have an app where you can study for the subject knowledge?
We offer some free subject knowledge test questions directly online (without app installation) here: https://www.sachkunde-34a.de/testfragen-pruefungsfragen-probepruefung-security/
Apps for preparation are available in the stores — here are the links to them:
Google Play (Android)
App Store (Apple)
Tip: Look for the ratings of other users. There are some free apps (with advertising) and also paid apps for a few euros. It is better to pay more attention to quality instead of learning with unhelpful or even wrong questions and answers.