Frisk was teleported to a strange room, and when he was told what was what, he agreed. Being in an unknown place and being asked about his life is not as bad as not existing at all. Moreover, in return, you told him what happened After he replaced himself with Chara, and erased himself from everyone's memory and from the timeline. He agreed to ask.

Frisk: "Soo...What do people from your world want to ask me?"