You will find a bleed screw on the slave cylinder mounted on the bell housing.
Clutches can sometimes be difficult to properly bleed because of the bends in the tubes and hoses and the volume, or lack thereof.
To begin with determine why it lost fluid. Most likely one of the cylinders is leaking. You need to determine which cylinder is leaking and rebuild or replace the cylinder. Also don't overlook the soft hoses which will sometimes fail.
Once the leak is repaired, you can usually bleed them with a helper operating the clutch pedal. If this doesn't work, put up a new post and we can offer some other procedures. I have done a few off the wall things in the past to get a clutch system bled.
Best of luck,