Just guessing, replace screws and bleed through the plug hole. I've done the same thing to my little floor jack I don't remember why , but jack works fine as long as it has oil. Maybe, extend the piston all the way Fill with oil and release piston with the plug out. When oil stops gushing out, insert plug. Jacks are just a hydraulic cylinder with a check valve. You tube probably has a how to. Good luck.