You can sort of wedge the screwdriver in there and pry it up. If you’re replacing it it really doesn’t matter what you do to that seal so long as you don’t damage the bearing surfaces.

I’ve been known to turn the powerhead upside down and slowly drill a hole into the seal, then use that as a prying surface.
I don’t think I’d recommend that for your first one, though. You have to plan it out so that you don’t get shavings into the motor.