When you lack evidence it’s ok to say “I don’t know”. It’s expected of people who do science. Cosmologists have for decades been doing mathematics, not science.

There is a theory that the big bang was not a one time phenomena and has happened more than once Therefore there can be multiverses

I only believe in things I see evidence of. This hypothesis is unproven, so I can’t say I believe it. However, is it a possibility? Perhaps is the answer to that question.

In order to have a (any) "belief", I look for actual evidence. So far, all I have read about is ideas (hypotheses) that, from a physics perspective, they could exist and may provide explanations for some phenomena.