Jack posted how to disassemble the axle. I'm not sure that's what you're asking.
On the GM axles/transmissions in our cars' era, there is an internal snap ring you have to get past on the install and the removal.
This youtube video shows it well - the "money shot" is from about 7 minutes in. See https://www.youtube.com/watch?v=9hHGgWJlPNU from Popular Mechanics.
HINT: the video is a little oversimplified. With the car in the air use a pry bar that fits and a square or plank of thin (around 1/4" thick it's not critical) particle board, plywood, or some such. Get the end of the plank up in there someplace you can get leverage and then pry the inner tripode joint housing. As you know, you can whale on the tripode housing but you CANNOT whale on the transmission case. The reason for that piece of board is to give you a good flat spot to pry against as well as keep you from chipping or fracturing the transmission case as you whale the joint out by prying the housing outward from the transmission. After you've removed one you'll be a pro at removal ha ha. If you're worried, just go to a pick-n-pull on a Saturday morning and practice on pretty much any 1995-2005 GM US-built auto transmission car. NOTE - Boy Genius in the video is using an indexable pry bar. They are like $30 at Advance Auto last I looked. TEQ TP82216. RockAuto has similar bars, a bit cheaper. If you can get enough room to insert and swing the bar, a $3.00 (yes, three bucks) fixed-hook pry bar from Harbor Freight could work. BUT If you're doing this sort of work, though, you just might want to get the indexable bar, for one you'll save a ton of time and headache on a variety of pop-it-off tasks and for the other - unless you have the car up on a lift you may not be able to get enough room to get the fixed-hook bar up in there along with the thin board. And admittedly, the solid bar is handy to have for messing with campfires and such in addition to automotive work. Oh one more thing - any reasonable prying bar that will fit should work -- the axle is in too tight to just pull off but not so tight as to require the worlds longest bar. The key is to have a heavy-enough bar that is small enough to get up in where it has to be, and to use the board to expand the surface you're prying against so you don't bust stuff up trying to pry out the half axle by the tripode housing.
As for what you tried -- the big screwdriver didn't work because there's no place to get it in and it's not stout enough for the leverage you need. A small crowbar won't work because it's just the wrong shape. Get a better tool and have at it again.
