Repairs can be arranged from Apple Authorised Service Providers, an appointment at an Apple Store or via courier. If you’ve already paid to repair this issue, you can contact Apple to discuss a refund for the cost.
Apple has got good at admitting manufacturing flaws in its devices of late and it’s good to see the company fixing phones that were made in such a small window. It also shows the market longevity of its iPhones that it was still manufacturing the iPhone 6s in August 2019; the iPhone 6s was launched in September 2015.
Take a look at the support page here if your iPhone 6s won’t turn on to see if you can get a free fix.