EDIT: Just forgot -> you should check first if the F1 fuse isn’t blown…
C93 & C31 are both 10µF capacitors. C93 could be broken. But afaik they seem to work as decoupling capacitors – so even if one of them (or both) are broken you should still see the unit powering up. It’s more likely the U5 regulator you’ve fried, since it’s rated for a maximum input voltage of around 6-6.5V… so you should measure if only the middle and the heatsink pin are connected to ground and if it outputs 3.3V.
U5 is a bit tricky to desolder (since the display is nearby) but it is an inexpensive part to replace:
After replacing it you should make sure all the 8 smaller regulators (U6, U7 etc.) aren’t fried and (therefore) shorted to ground too before powering up the OSSC again.