take to a mobile phone shop if u are not confident to do it yourself..
what i can tell.. is take a screw, cut of it's head.. solder the head to the faulty screw.. then happyly use screwdriver to remove it.. and change to new one. easy rite?

hahaha.. actually it's common thing that mechanic do.
once i tried to change my bike engine oil by myself.. but what happen is i accidentally broke a screw on the oil filter cap. the screw stay inside and the screw head fall down.. quite nervous at that time coz i tot it may not be recovered. go to shop, get a lorry and bring my bike to the shop, then what they do is they did as what i told u earlier.. whoaaa.. lucky.. the screw can get out. hehehe... thank god. now i never change my bike engine oil myself again !