Ahem, another "relic" checking in here...
The NCR Tower ran AT&T System V, not Xenix. You need to keep that ADDS terminal since the software needs to run curses based programs with a limited number of supported terminal types.
It's been almost 15 years since I've seen an NCR Tower and I don't remember enough about them to be helpful. However I have a TOWER 32/8XX Support Student Manual dated 1989. It is very terse, but I might have a procedure that may work. You will need an OOS tape to do it. These instructions are for Release 010100 by the way.
"Press the RESET button on the System Control Submodule on the Master AP." I seem to remember opening a door to expose all of the cards to reach this switch, but I'm not sure.
You should get a menu "Select Start-Up Function". Select "1. Load". You will be asked for the load device and you need to use "st00". You should now see a "System Loader Functions" menu. Select "5 Load Out-of-Service System". This should give you a list of terminal types. Pick yours.
You should get a OOS menu. I think "3. Service Utility Shell" is the best choice. You want to get to a bourne shell prompt. Now you need the name of the root disk. If you don't know, try the default:
mount /dev/dsk/10s1 /mnt
Now you need to fix /mnt/etc/passwd to change or remove the root password or create a root equivalent account with no password.. Exactly what you do depends on what programs you have available and I don't know what you have at this point. Any unix expert should be able to take it from here. Good luck.