Follow the steps below :-
1, Click Start, point to Programs, Microsoft SQL Server, and then click Enterprise Manager.
2, Expand Microsoft SQL Servers, SQL Server Group, Microsoft Project Server database server, and then expand Databases.
3, Right-click on the Microsoft Project Server database, after that click Restore Database.
4, From the backups lists, click the backup to restore, and then click OK
5, Click OK to ensure that the restore process has completed successfully.