Travel Through Time and Space to Do Tasks

"Young man! Do you want to give you a super power?" An old man was persuading a young man, but he said: "No! Get out!" Seeing that the young man was kind-hearted, the old man gave him the ability to travel through time. "The other world is calling you, come on, young man!" (The title of the book has been changed, and the cover cannot be changed now, sorry)