Science can't tell us anything about how to be more rational? Is that your claim?

I think the claim is that science can't tell us how to become "perfectly rational". Science can certainly tell us how to become "more rational", but only if we already have a specification of what "more rational" is, and just need to figure out how to implement it. I think most of us who are trying to figure out such specifications do not see our work as following the methods of science, but rather more like doing philosophy.