Apple is starting a service program to repair iPhone 6s and 6s Plus units that may refuse to power on due to a component that could potentially fail. Apple doesn't disclose which exactly component is prone to failure, nor does it detail what the service operations are going to be. The affected devices fall within a limited serial number range and were manufactured between October 2018 and August 2019. There's a serial number checker on the program's web page, and should you be among the unlucky ones you have three possible courses of action - find an Apple Authorized Service...
Source: https://www.gsmarena.com/apple_initiates_service_program_for_iphone_6s_and_6s_plus_units_that_wouldnt_power_on-news-39502.php
