Should you update an existing page or create a new one?
Update the page that already covers the topic when the question fits it. Create a new page only when the question needs its own substantial answer.
If a visitor asking the question would naturally land on an existing page — for example a service page — adding the answer there keeps related information together and avoids several thin pages competing for the same topic.
Create a new page when the topic is distinct, needs more than a short paragraph, and would be useful on its own. Mass-producing near-identical pages for every town or keyword is the kind of 'scaled content' Google's spam policies warn against.
If two pages end up covering the same thing, Google's guidance on canonical URLs explains how to indicate the preferred version.