Open the Microsoft SQL Server Management Studio. Right click on the database name, select Tasks and Back Up..
Under Destination, click on Add. Enter the file name. As example, ITsiti_1.bak
Click Add again to add the file name with the sequence, similarly like below. It depends to you, on the size to be allocated to each file. If your database backup is 2TB and you split into 10 files – each file will have 200GB.
Click OK and the backup will start accordingly.
