Do not worry, that's pretty easy. To change the language of the app please do the following:
1. Go to Settings on your device;
2. Scroll down to the list of all apps on your device and find Prequel;
3. Tap on Prequel;
4. Go to Language;
5. Select your preferable language from the list.
You can also switch language directly in Prequel. To do this, please,
1. Enter Prequel;
2. Tap on Settings (an icon in the right upper corner);
3. Tap on 'Languages' (if, accidentally, your Prequel is on the language you do not know, tap on the 5th line);
4. You will be automatically transferred to the Settings;
5. Tap on 'Language';
6. Select your preferable language from the list.
One more tip: if the option of selecting the language is not available, please do the following:
1. Go to Settings on your device;
2. Go to General;
3. Tap on the 'Language & Region'
4. Add any other language to Preferred Language List.
That's it.