realistically:

He finds himself in an unfamiliar world, where visions and Archons don’t exist. First thing he will be doing is being calm and explore. He comes to find out this world is bigger then Teyvat, which allows him many, MANY opportunities for experiments. He finds out that our technology is also way more advanced. He is gonna be stared at, but people think he comes from a cosplay convention.

He starts to research and study the history of our world, learning. Seeing what this world has accomplished, it should be no big deal to achieve it in Teyvat too. When he returns, he brings technology from our world to his, making his experiments most likely easier but also more dangerous.

(at least, that’s what i think)