To restore MSSQL please follow th following steps :-
1) Login to Plesk control panel
2) Click on "Domains" and then "Domain Name" .
3) Then click on Backup Manager.
4) Now click on "Database Backup Repository" and select the required
backup file from the list if you have uploaded the file.
NOTE :- If you do not have the backup file on your server, you can upload
the backup file to the server repository from your local machine
5) click Restore Selected.