How to allow window background service to access SQL Server database?

I have background service which access my SQL Server database开发者_运维问答.

My background service working fine when I try to get a row from SQL Server database I get an exception

base {System.Data.Common.DbException} = {"Cannot open database \"test2\" requested by the login. The login failed.\r\nLogin failed for user 'NT AUTHORITY\LOCAL SERVICE'."}**

test2 is my database name.

How do I allow my background service to access SQL Server database?

grant user NT AUTHORITY\LOCAL SERVICE access to the database