Option 1:

1. Go to the Settings app on your device.
2. Find the Content Office app through search.
3. In the «Preferred language» section, tap «Language» → Select a language from the list

Option 2:

1. Go to the 'Settings' app on your device.
2. Next, go to “General” → “Language and Region” → “iPhone Language” → change the language and click “Done”.
3. Exit the Content Office app background. Log into the Content Office app again.