How to add a NFT to Metamask:

Step 1 : Find your NFT's contract address. 
On most NFT interfaces, you will find a value labeled "Contract Address".

If you click on this, it will take you to the contract's address on Etherscan/BscScan/PolygonScan; at the top-left of that page, there should be an icon labeled "Contract", and to the right, a long string of letters and numbers. 
This is the address of the contract that created your NFT. Click on the "copy" icon to the right of the address, and you'll have it on your clipboard.

Step 2: In MetaMask Mobile, tap on the 'NFTs' tab, scroll down, and tap on the "Import NFTs" link. Paste the NFT's contract address from your clipboard into the "Address" box.

Step 3: Find the NFT's ID. A collectible's ID is a unique identifier, since no two NFTs are alike. You can find the NFT’s ID under "Token ID" on the NFT’s page. Copy it!

Step 4: Paste the ID into the box marked "ID" in MetaMask Mobile, tap on the "IMPORT" button, and your NFTs should appear under the NFTs tab.