You can restore SQL .bak file with few simple steps to process the same you will be required SQL Server (As you are using local server) & SQL Server Management Studio (SSMS).
Please follow the given steps.
1- Launch your SSMS and connect it to your server.
2- Right-click the Databases node in Object Explorer and select Restore Database.
3- Select Device, and then file location in your device.
4- Select your SQL .bak file
5- Select OK to close the Select backup devices dialog box.
6 - Select OK to restore the backup of your database.
Alternatively, you can run the following Transact-SQL script to restore your database. The path may be different on your computer:
RESTORE DATABASE [SQLTestDB]
FROM DISK = N'C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\MSSQL\Backup\SQLTestDB.bak' WITH FILE = 1, NOUNLOAD, STATS = 5;