Hey hey! So your copy of Beat Saber won't automatically be on your headset, but you should get a notification and an email in order to redeem it, that way you don't have to pay for it!
Once you activate your new Quest 2 on your account, you should get an email that has a link to follow to redeem your copy of Beat Saber to your account. (If you don't see it in your inbox, make sure you check your junk/spam folders too.) Once you do that, you should be able to install it on your headset!
Hope that helps! Let me know if you have any questions at all. 😁