Hi ameetagarwal2010,
To add the slider and replace the default slider then it needs code customization. The file is inside theme folder-> inc-> structure-> header-extension.php
You have to customize the code. But before making any changes in it first of all create a child theme and then only customize the code to be safe from data loss while updating to our new version. If you are unable to fix it then you need to hire a developer to fix it.
Thank you!