I assume you have the Blackbox (Steam gauges) King Air ?
I did a similar thing, played with the mixture mid flight…cut both engines and then took a close look at the scenery!!!..took me a while to sort it out and get the engines started and back in the air again.
Had to restart the flight on the ground somewhere, ‘repair’ the engines using the failure options in the weather radar.
Then work through the start up carefully making sure all was ok …if you mess up the start again you may damage the engines…so keep checking in the failure system!