This feature works only for ETH NFTs that are not on sale. It will be wrapped via the linkdrop.io service and then it can be sent to other wallets.
You can access this option on the profile page from Rarible web. It is available in the 3 dots menu for every NFT asset and has a NEW label next to it.
Rarible is a popular NFT marketplace that is operated by a DAO that supposes to get an Android app soon.