[Thinkpad T420] The screw holding the shell with the CPU won't come off

[hi im cool]

Hi, first time posting here so i'm still new to this, mb if my explanation sounds bad.
so recently, i got this T420 and i wanted to clean the CPU and fan/heatsink but this screw connecting the shell wouldn't come off.
i tried using my Phillips #00 and #0 on it and it wouldn't move despite being able to fit inside it.
is there something that can be used to open this screw?

[RealBlackStuff]

Try a small, strong, flat screwdriver diagonally in the screwhole.
Or a pair of pliers.
Or tape everything around it up, then use a Dremel with a diamond disk to make a small groove in that screwhead.
Then use a flat screwdriver to first slightly tighten it (yes), then try and get it out.

[hi im cool]

Try a small, strong, flat screwdriver diagonally in the screwhole.
Or a pair of pliers.
Or tape everything around it up, then use a Dremel with a diamond disk to make a small groove in that screwhead.
Then use a flat screwdriver to first slightly tighten it (yes), then try and get it out.

Hi sorry for the late response, i tried the pliers and it worked in getting it out, thanks