Find the NFT's address.
If you click on this, it will take you to the contract's address
on Etherscan; at the top-left of that page, there should be an icon
labelled '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. In MetaMask Mobile, tap on the 'NFTs' tab,
scroll down and tap on the '+ ADD NFTs' link. Paste the NFT's
address from your clipboard into the 'Address' box.
Find the NFT's ID. A collectible's ID is a unique identifier since no
two NFTs are alike.
Make a note of it, or copy it onto your clipboard. Paste the ID into
the box marked 'ID' in MetaMask Mobile, tap on the 'ADD' button, and
your NFTs should appear under the NFTs tab.
Check out the following guide