I have paid $5, but I did not have an itech account when I made the payment. My PayPal account is 1030887710@qq.com, and now my iech account is 1983385659@qq.com, but my library is empty, even though I Use the email address of the PayPal account to register the itch account, the library is also empty, and I can't find any download links.

Hello! You would need to connect your Patreon and Itch.io accounts first, to be able to download the package for free, here:
https://studiominiboss.itch.io/pixel-art-tutorials/patreon-access