Changing Default Database File Locations in SQL

I missed to specify the default location for the data file and the log file while installing SQL SERVER . So when I created a database and did not specify the default location for the files it will be created on the location defined in the server settings. So if we want  always the data files and log files to be created on a particular location we can
change the server properties through SSMS - > Database Settings -> Database default locations .

However this requires the sql instance to be restarted for the changes to take effect.

Adding missing permission to a folder for the MSSQL$instance account

I had to move the data files from one driver to another. After moving the data files when I brought the database online it gave"Access denied" error and I found out that the reason was that the MSSQL$instance account did not have permission to the data file.
I right clicked on the folder and on the security tab tried to add the user to give the missing permission but could not locate the user. I had to do the following to find the user in the user list

To add the missing permissions
chose the local computer and type in "NT SERVICE\MSSQL$instance