Time existed since the big bang so there's no concept of before the big bang.

Some people interpret this as time being in a loop, kinda like if you were to walk around the earth, you will end up at the same place at some point and start again.

We might be living in a multiverse, where this universe is just a tiny part of it, or there could be multiple universes running at the same time.

The truth is that we don't know yet, and maybe we will never know.