I have already done a true pacifist run and my save is at the part before you go to the surface (human world). I searched online on how to get to Sans' room but I'm confused.

"To get the key to his room, you need to do a True Pacifist run. Do the whole run until you get to Sans' judgement in the Judgement Hall/Last Corridor. (Before Flowey & Asgore) There is a savepoint before this talk. Let him finish his speech, and after he vanishes, reload. Then talk to him again"

I have tried loading my save and going to the corridor but Sans isn't there because he is with the rest of the gang before the savepoint to say goodbye. Do I need to do another pacifist/true pacifist run to get the key. I have no idea, please help.