I'm not teling you where (I've just found out), would you like to know where it is, or you already knew? (it' in the same place as like, dislike and add to playlist)
Don't have thatGo to youtube settings tab, set autoplay to on. Play a video, swipe it to almost end..,wait a sec. When it ends, it will zoom out a bit, and you'll see "play next" on the right, and below you'll see "related" and "more options". In "more option" , you'll have : go to channel (where you can subscribe) like , dislike, add to playlist and report.
Here is my video about it.This needs to be a video tutorial because I can't get it to work.