If you’d like your existing collection to appear on OpenSea, follow the requirements below.
Stay as close to the OpenZeppelin templates as you can.
Implement OpenSea's metadata standards.
Add an "Ownable" owner function as the primary system of contract ownership. You can learn how to implement the Ownable standard on GitHub.
Collections will be automatically displayed on OpenSea after at least one NFT is minted.
You can find more information about developing on Ethereum in the developer resources published on ethereum.org.