Link Track / Song

There was a guy who created a video on YouTube sometime back that I can’t seem to locate and now I’m reaching out to everyone here to see if I can get some help and or Support, he loaded a track into a deck, and was able to link another song to that particular track, so that every time he pull that particular track into a deck, it brought up the related song that would mix perfectly that he selected with that particular song, I don’t know where the feature is located, but I have been searching, and hopes now reaching out to everyone in the community, that someone will have some idea how to make that work, it’s not the next recommended song, but it is a song , as he explained it, when two songs that you know that mix perfectly together you were able to link those songs so every time you load that particular song, it will bring up the song you recalled that makes perfectly with that particular song, does anyone here understand what this means, and knows how to do that or can show me that feature or can tell me how to locate that feature, I have been looking with no results everyone’s help is greatly appreciated