How Unscrew an H Type Screw
 H Type Screw

Ιn this way you will be able to unscrew H-type screws in electrical appliances

self drilling screw

dremel

caliper (optional)

with the dremel shape the screw

flatten the screw end

reduce the thickness of the bit until it is equal to the thickness of the screw slot

make a notch in the middle corresponding to the depth of the screw