I figured there must be a lot of science fiction about scientists creating universes. In 15 minutes of searching I only came up with two that I didn’t know about:

The Last Question by Isaac Asimov (1956) – In this one, people and computers are trying to figure out over many generations what to do when the universe ends. I won’t spoil the ending.

Schild’s Ladder by Greg Eagen (2002) – I think this one is about a universe accidentally created by scientists. There is a plot summary on Wikipedia but I didn’t want to read it and spoil it for myself.