MacBook Pro 2015: Blank screen after screen replacement?

I've just replaced the screen on a macbook pro 2015, with a second hand screen.

You can hear the device booting up but there is no display. Unfortunately I followed a youtube video that never mentioned disconnected the battery - wish I'd done more research so I'm worried components are fried. The macbook was powered off.

Is there a way to know if the screen is functioning as it was second hand?

I was considering attaching the old broken screen to see if it still displays incase I've fried some components.

Thought I would ask here before I done anything else, really appreciate some advice on what to do next.