The answer to "where did the Big Bang happen" is always "exactly where you are", no matter where you are. This is because it's not an event that happened in the universe, it is the universe.

Unfortunately I can't find the GIF with the expanding red dots that made it clearer, but the idea is that there is no preferred reference frame and thus no location that's "more important" than any other.

This image might help. Picture A is the location of galaxies at some given time, while Picture B is the location of galaxies at some future time. Pictures C and D show that the galaxies appear to be moving away from "here", wherever "here" might be, and the galaxies farther away from "here" appear to be moving faster.

https://allthatsinteresting.com/wordpress/wp-content/uploads/2013/03/big-bang-dots.jpg