Once you have logged in to your dedicated server as root via SSH, go to the folder where the dump file of your database resides. Once in it, type the following command to import it into the selected database:

mysql DATABASE_NAME < BACKUP.sql

Change DATABASE_NAME with the actual name of the database into which you want to restore the backup.

Note that if the dump file of your database contains a "CREATE DATABASE" clause you will have to delete this line from the dump file. Since it contains only plain text, you can use any text editor to do that.