If you are using the device without modification, you can navigate by translating the Japanese labels:
Many users rely on Google Lens to translate the screen in real-time using their phone’s camera. Community Solutions for English Conversion
This specific label is where language toggles would typically exist, though it may only offer Japanese on stock units.
Since no official manual exists, the "hacking" community has developed ways to partially or fully convert the UI to English:
Because the AVIC-MRZ09 was not intended for export, the system language is locked to Japanese by default. Unlike international Pioneer models (like the AVH series), which often have a "Language" toggle in the settings menu for five or more languages, the MRZ09's menu structure remains entirely in Japanese unless modified.