You'll need a spanner wrench to handle the task. They're available on line, and you can probably find a decent set on eBay. Be sure to get one with interchangeable tips, because the spanner wrench is very versatile. They work on lens retaining rings on view camera lenses, and sometimes, even on watch backs when you need to change batteries.
Alternatively, you can grind part of the tip off a flat blade screw driver, and taper the points to fit the two holes.