You've got the right hole m8

Its a flat screw in there,not philips.As above though,could well be seized

Setting the base idle is the thing you can do yourself without having to go buy any bits

Not sure it will sort your problem though,because your ISCV should be lifting the idle speed when the car is cold

Have you tried disconnecting the ISCV when the car is hot and its ticking over at 1200rpm,what happpened????

If the idle droopped back to 850rpm you have got electrical/ISCV problem