Password should be on the rear, or in the original instructions.
If not, you have to Reset it and then set it back up.
Mmmm, that model number comes up as a phone not a router. Here is your user guide, so have a read.
[PDF]1408/1416 User Guide - Avaya Support
Avaya 1408 and 1416 Telephones - connected to Integral Enterprise - User. Guide. 16-603463. Issue 1.09. January 2010 ...
Jan 14, 2015 - If your telephone system includes a voicemail server, pressing the key messages MESSAGES button accesses voicemail. Your system ...
Nov 6, 2015 - 1408/1416 Phone User Guide ... Avaya reserves the right to make changes and corrections to the ..... 7.2 Manual Account Code Entry.
Avaya model 1416 D02A Google Search