Start by checking the fuse and wiring connections. If those look good, use a multimeter to check whether power is reaching the display. If it is and the display still won’t light up, the meter itself may be bad. Hope this helps!
Could you post a picture of this LED panel.? Is it a stand-alone gauge for battery voltage or is it an engine associated panel that shows battery voltage or alternator output? What brand engine?
It's a common problem. The meter is bad. You can't get the exact meter anymore. You have to order a kit. You'd have to cut the panel to make it fit. I chose to live with it. It says 120VAC maybe put a sticker one it if It bugs you.