To Import MSSQL Databases in Plesk 10.x, please follow the following steps :-
1) Login to Plesk control panel.
3) Click on "Websites & Domains".
4) Click on "BackupManager".
5) Click on "Database Backup Repository".
6) Click on "Upload Backup File."
Note : You can upload only .bak file only.
7) Click on Browse to select the .bak file from your Local computer
8) Click Ok.