This is one of the questions that many secular people will ask.This is one of the questions my brother used to ask.He was a scientist.What would you tell them?
I would say that the concept behind proving something by the scientific method, is to develop a hypothesis, and then prove it with repeatable experiments to see if nature does what one thinks it should do. HOWEVER, anyone who is truly scientific can see that the scope of that proof lies in the advancements and technology of the day. In other words, there's some "experiments" that cannot be done, so a hypothesis remains just that: a hypothesis. A truly scientific person will agree that there's limitations to what can be proven. In that case, anything that cannot be proven remains
inconclusive.
Now, if this is a question (in disguise) about using science to prove if God exists and one's right to believe, then again, it cannot be proven. They may create a hypothesis saying that an intelligent being would react consistently to one's experiments (such as answering prayer 100% the way the person wants it to be answered), but this is a logical fallacy, for maybe God does not react the way we hypothesize. This is the same erroneous logic as a burglar who rings a doorbell (analogous to praying) and if there's no answer, then he must not be home (there's no God). No, maybe the guy was taking a shower, or didn't hear the bell, or maybe just does not care to answer the door. Many confrontations occurred because of the crook's uppity, arrogant assumption.
Also, one who places too much faith in the limited scientific method is blindly believing in that over placing faith in something they accuse cannot be proven, and in effect called the kettle black. When I discuss anything with atheists, I always say that if they were truly, truly honest with themselves, they are really
agnostics, i.e. one cannot prove (by their standards) whether God exists or not. So one therefore has every right to believe or not believe because either position lacks the evidence they so much crave. That's because sometimes things do exist that cannot (at this point) be proven and sometimes they don't.