Ironic request given that we have to exist to use science. And we humans make observations, science is a method and has no senses.Can you with science explain how we observe that we exist as exist?
If you are stuck in the mud struggling with existential questions you will make no progress. It is apparent that making progress in knowledge is itself confirmation that we exist. There's an irony in the uncertain loop questioning whether we exist, because who is it stuck in the thought loop?