When you receive the new phone then launch the Samsung Members App on that phone and the link to make the claim will be at the top.
If you've ordered the phone via a Network then your going to need the Proof of Purchase from them to provide to Samsung to validate your order.
Typically also their are eligibility dates to make your claim by so make sure you claim in good time. See below.
when you pre-order the new Galaxy A52s 5G. Limited time only!*