Assign a User to Be Database Server Admin

As a rule, Database Server Admin is considered to be a user who installed SQL Server. Other users can become Database Server Admins in case the Server Admin assigns them either when installing SQL Server or later by adding them to the "sysadmin" SQL Server role using one of the following methods:

SQL Server Management Studio (SSMS)¹⁾ is not installed on the computer (by default).
Video Instruction:

Text Instruction:
Run as admin Command Prompt and run the following command:
sqlcmd.exe -S СерверБазДанных\Экземпляр -E -Q "CREATE LOGIN [Domain\Login] FROM WINDOWS; ALTER SERVER ROLE sysadmin ADD MEMBER [Domain\Login];"
- Replace DatabaseServer\Instance with the database server name and the name of its instance (it’s the computer name and "SQLEXPRESS" by default);
- Replace Domain\Login with the user account domain and login.
SSMS²⁾ is installed on the computer.
Video Instruction:
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Text Instruction:
1. Start SSMS.
2. Connect to the selected SQL Server instance.
3. Select the "New login" command in the context menu of the "Security\Logins" folder in the Objects Explorer tree.
4. Do the following actions in the opened window:
  1. Specify the account name in the Domain\Login format in the "Login name" field on the "General" tab
  2. Check the box next to "sysadmin" role on the "Server roles" tab and click "OK".

¹⁾ , ²⁾ SQL Server Management Studio (SSMS) is a free of charge software that can be downloaded on the Microsoft website.