How to add a populated field to a finished sql table?

Question

SQL Server

There is a table from one field, already filled. How to add an ID field to it with a key, an identifier that will automatically fill in to those lines that have already been entered, and, of course, automatically filled in when new brands are added?
MARK | ID
--------------------
Nissan | 1
subaru | 2
Toyota | 3
Tried via alter table marki add id int not null primary key
This adds a field but the values ​​of already existing rows are null

Answer 1

alter table marki add id int not null identity(1,1) primary key