add identity column to Access Database

I have an Access 2007 database that I am trying to work with, and the previous creator made some design questions that don't make sense. there are about 15 different tables, and none of them have identity columns. The primary key was designated using the nvarchar data type.

I understand how to add a new column, but need help with going through each item in the table and assigning an ID.

Cheers,
Brendan