save the following 2 lines
EXEC sp_change_users_login 'Update_One', 'privuser', 'privuser'
EXEC sp_change_users_login 'Update_One', 'pubuser', 'pubuser'
in a .txt file and renanme the file to a .sql extension
open the file with MS SQL Management Studio (double-click it)
or
open MS SQL Management Studio (Start \MS SQL\Management Studio or
"C:\Program Files\Microsoft SQL Server\90\Tools\Binn\VSShell\Common7\IDE\SqlWb.exe")
you will have to:
- login to your SQL instance using SQL sistem administrator (sa) password or Windows authentication (if logged into Windows with an admin user)
-
make sure you select your P6 database (ex: PMDB or pmdb$primavera) in the pane on the left.
- under File menu either Open and navigate to the file or New Query (Ctrl+N) and paste the contents of the file
IMPORTANT!
this is pretty harmless and simple but other scripts may cause you to lose or permanently trash your data!!

BEFORE running querries it is recommended to back up your database (if you are't sure how it is better not to run querries at all (simple or not)!!
- execute the 2 querry lines (F5). you can select and execute selected query/ies separately if you need to.
hope this helps