First, if you don’t have it already, you’ll need to add Polygon Mainnet to your MetaMask Wallet from the drop down (where it says Ethereum Mainnet). To do this, follow the prompts as shown above.
Next in your MetaMask wallet select ‘NFTs’ followed by ‘Import NFTs’ as shown above.
You will be prompted for the NFT address and the token ID. On OpenSea find the NFT address and the token ID under the ‘Details’ section on the listing for the NFT as shown below (you’ll need to expand the Details tab to see them).
Input the contract address and Token ID into the fields shown in step 3. For the contract address you’ll have to click the link (as shown above) and then select the copy icon as shown below.
🎉 Congratulations you can now see your Polygon NFTs in your MetaMask wallet.