Use an easy-out. It has a conical head with left hand threads.
No ! Please, please do not use easy-outs for they are the spawn of Satan - When you break one, you have to pay an exorbitant amount to get someone to spark erode the remains out - I've wasted more than enough time dealing with the aftermath of these damned things.
Most likely it is no more than an M3 screw, so carefully drill the whole thing out.
With an easy-out that small you really don't stand a chance of getting it out. Just take it to a machine shop or your nearest mechanics shop. I am sure they can help out out better than doing it yourself. I know because I was a Machinist in my working days. You may f**/ it up REAL good. Leave the delicate work to the proffesionals.