If there's a voicemail tree on extension 8892. The 2 tree extensions you need to record on might be 5892 and 5893.
To set up the individual greeting, from a district phone, do the following:
5892 (or 5893)
0000 (default passcode)
and then follow the tutorial.
The initial greeting of "press 1 for.... press 2 for...." on the main number (8892 in this example) will be automatically generated when you set up the 58xx tree extension numbers.