@Amit-Kamble Have you purchased Sound Forge directly from Magix.com? You should have gotten an order confirmation e-mail instantly after purchase and can find your serial number there. Please check your e-mail Inbox and especially your spam folder.
@Amit-Kamble Then you need to contact customer support at infoservice@magix.net. Try to write as much information as possible (your name, e-mail address, purchase date, which software you tried to purchase etc.), so they can look it up in their database and don't need to ask you for it.
It can take up to 3-4 working days until they'll respond
If you ordered directly from Magix online, you can find the serial number under "My Account / My Products."
Go to: MAGIX Service Center – Login to your account
Good luck,
Rob
This only works if you bought an upgrade. New licenses will not get automatically registered in the customer account. Here you need the order confirmation e-mail and register the serial number manually.