Stuck headset bearing

lots of WD-40 (soaked, more than once of needed, upside down) and a flat head screwdriver used as a scalpel sideways, tapping with a small hammer. 

change point of force, don’t tap always in the same point of the circumference of the bearing.

WD …. as its the most common solvent found in everyone’s tool kit.

Basically, the cartridge bearing was installed dry, so the steel outer race has galvanized to the aluminum head tube.

Prying it with a screwdriver to forcefully will end up deforming sections of the headtube.

Ideally, using something like Chill Zone from Finish Line. It’s a great way to unstick the two alloys.
It’s readily available online (most shops don’t carry it, though it’s a great go-to in cases like this.)

If you end up prying it, just be patient and don’t force it.. several round of gentle prying around the circumference of the head tube will eventually unstick the bearing.