Adding NFTs in the MetaMask Mobile App:

In the wallet, go to the "NFTs" tab and tap "Import NFTs".

In the first line, enter the address of the NFT smart contract (in this example, we'll use the Cosmic FOMO NFT address): 0x587cBe061e96a425a60a637f430C2b20e6dA7A86, and in the second line, the ID of your NFT, then tap "Import".