If you're still using the same browser where you made the wishlist, sign in there and it will move to your new account. If you made a recovery link or email earlier, use that. If neither is true, the wishlist can't be recovered.
When you make a wishlist without signing up, it's owned by a temporary guest account tied to your browser. Getting it back depends on whether that browser session still exists.
Steps
Try these in order.
Are you in the same browser on the same device? If the guest session is still there, just sign in (Google, Facebook, or an emailed magic link). The wishlist links into your new account and you become the owner.
Did you save a recovery link or email earlier? While you were still a guest, you could create a recovery link or send yourself a recovery email. Open that link to claim the wishlist. Recovery links and emails stay valid for 365 days.
Neither? There's no way to recover it. The section below explains why, and how to avoid it next time.
Why this happens
The link transfer only works in the same browser that still holds your guest session. Clear your cookies, switch devices, or open a private/incognito window, and that session is gone — and so is the automatic transfer.
That's why a recovery link or email is your only fallback once the browser session is gone. You can only make one while you're still the signed-out owner of the wishlist, so set it up before you switch devices or clear anything. One limit worth knowing: a recovery email can't be sent to an address that already belongs to a registered Wishpicks account.
If you reserved a gift as a guest rather than made a wishlist, that follows the same rule. See "If I reserved a gift as a guest, will it move to my account when I sign up?"
The safest move is to sign up early. Once your wishlist lives on a real account, it's tied to you — not to one browser — and you can sign in from anywhere to get to it.