Did you get the TV fixed after it was plugged in and it turned off all the lights, you didn’t say?
When the higher voltage power supply was connected to the TV which requires a lower voltage supply to work it would have damaged the power board in the TV. It definitely would have blown a fuse on the board and probably also damaged some other components as well. Connecting it to a step down power supply now would have no effect as the TV is damaged and needs to be repaired first, then you can use it connected via the step down power supply.
If you don’t know much about electronics you may have to get a reputable, professional TV repair service to fix it for you.