Mine had a tommy bar as it's keyring so it's always to hand .... an old scrap screwdriver with the right shaft diameter and the end cut off will do to put into the hole for leverage ... also the blunt end of a drill of the right diameter (but wear sturdy gloves to protect from cuts... or breakages if you're really strong)
Sometimes gently flexing the screen as you turn will loosen things up ... a thin smear of grease on the shoulder that locates in the screen bracket will help for next time.
K
