How to power on nintendo switch with a dc power supply？

I have a customer’s nintendo switch which wont turn on, wont charged and cannot enter the RCM mode (for testing purpose), i am not sure what the problem is.. I have tried to swapped the battery, but it still didn’t work. It only showed the Nintendo logo for a split seconds then shut off.

I have a bench power supply, but I don’t know where to connect it - i want to test the console as i dont have a spare battery. Does anybody know how to do it?

Thx