Ask them for examples.....
The scientific method is only about 200 years old and has only really been applied to research and progress for about 100 years.,In that 100 years we have gone from horse and cart to lamding laboratories on comets.
When someone says 'people once said the early was flat' that is irrelevant to the term science. Whilst people were saying this, some people were using geometry to calculate the circumference of the earth to three decimal places, this was relevant to science.
These people won't be able to define science and won't have examples of science changing, Evidence does not change, evidence is added to and can have various interpretations. science is the gathering of evidence and of course as we gather more we learn more and our interpretations can increase.
The staple test to see if science is a valid method is to see whether it works...does it answer questions and solve problems? it clearly does.
Read them the scientific method. Explain who a scientist is. Explain the difference between newspaper articles about anacdotal opinion and 10 year random controlled trials, double blinded, with results indicating 'x'.