If you've forgotten your Access Code, as of RM firmware 6184, it can be reset to the default “12345” by holding down both the +48V meters button and the Main headphone source button for 15 seconds while booting the mixer. NOTE: Prior firmware versions can only reset the Access Code by doing a Firmware Recovery Factory Reset.
See this article for more helpful information: http://support.presonus.com/hc/en-us/articles/210047413-Default-Access-Code-for-iOS-Computer-Permissions