you could take each caliper off the fork-leg - one at a time. Pull the pads out. Then pump the lever once or twice just to see if all pistons are moving. If they are - good, If not - you will have to check the condition of the piston & seal that is not moving.
If they are all moving - there is a real easy way to pump the air out of the system. Take the m/c cap off and soak out most (not all) of the fluid. Then use a small G-clamp to compress each piston back into the caliper until it bottoms-out. Don't squeeze the shit out of the clamp - just turn it until you can feel the piston reach the bottom. Do this for all pistons (its a pain in the arse for 6-piston calipers

). What you also need to do is keep a real close eye on the fluid level in the m/c - as you push each piston back into the caliper, fluid will travel up the line and into the m/c. You may need to soak a bit of fluid out each time so it does not overflow.
Once you do a complete caliper - re-fit the pads, bolt the caliper back in - and then do the other side the same way.
When the other side is done - check the level of fluid in the m/c and top-up as needed. You should find that you can pump the lever once or twice - the fluid level will drop pretty quickly so keep topping-up - and after maybe 6-8 pumps - you should have good lever pressure.
This method pushes every bit of trapped air out of the lines and back up to the m/c. It is a bit more fiddly with 6 pistons but it works