This Windows user needs to be granted access to SQL Server and that specific database. It is usually configured during installation process of SQL Server. You can still do it by opening SSMS and adding this user under Security -> Logins node from Object Explorer panel.
Of course, to be able to do above, you need to connect to your SQL Server Express first. You may need to use another Windows user or a SQL Server user. The latter would be possible only if SQL Server Authentication has been enabled during installation process by choosing Mixed Mode for authentication (Windows + SQL Server).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…