If you are trying to add an NFT transaction manually or want to search for a specific NFT on the Transactions page then you will notice that it's difficult to find the specific NFT that you want to select.
Ex: Searching for Cryptokitties results in a list of 70,000 tokens. Note that all of the different NFTs share the same address since they are from the same collection:
You can now search for a specific ID by searching for the contract address and then writing the ID of the NFT:
[contract address] #[token ID]
The ID of your NFT can be found on the block explorers if you don't know it. Every NFT within a specific collection will have a unique ID.
If I wanted to search for my NFT called Cryptokitties with the ID 999914 then I would need to locate the contract address of the NFT.
I can do this by looking on Etherscan or any other block explorer and copying the address.
I then paste the address in the search bar followed by a space and then the ID (with a hashtag/pound in front):
It is also possible to search only for the token ID but this is only useful if the ID is long since common IDs will result in a lot of matches: