You can buy replacement glass and solder it in or a whole new display.

https://ksarcade.net/williams-7-digit-numeric-display-c-8364-1.html

Glass alone will be $70, so you may want to just buy the whole display.

First, make sure it's the display.
Swap the Player 3 and 4 displays and see if it is still out.
It might also be a ribbon cable, or a problem with the display driver.
If it is the display that's out, you can also try to find a working used display on here.