Log in to a system administrator's mailbox, after inputting the security code press 0 to get to administration options. Things like resetting a VM box security code, deleting messages/mailbox/ adding new MB, recording greetings, etc.
As for coosessions, set dip switch SW2 position 3 to off. Press VM reset button SW1 (at the top by the card puller tab). If your VM card does not have that witch, then use the make busy slide switch on the front dege of the card. Make it busy and WAIT until all LEDs stop lighting or flickering. Then set it back. After the VM comes back on line you should be set to connect locally. Use a 9-9 pin straight cable. You may need to try several baud rates. Start with 9600, then 14400, 56K.