How to mint a nft into an existing collection?

[delight-ng]

How to mint a nft into an existing collection by its address?
For example, here you have to set the parameters of a new collection, and if it exists, you get an instance of it.
https://github.com/tonfactory/tonsdk/blob/master/examples/tokens/nft/mint.py#L13-L19
But I want to use a collection created without this library.
And what is NFTItem.code, why does it have a specific value?