You mean how to bleed the system? Not sure why you want to flush the PS. To bleed (which you need to do anytime the power steering fluid lines have been disconnected):
With the front wheels straight, fill the power steering to the cold mark.
Start the engine and run at a fast idle, then recheck the level and add more if necessary, to reach the cold level.
Bleed the system by turning the wheels from side-to-side, without hitting the stops. This will work the air out of the system. Keep the reservoir full of fluid while this is being done.
When the air is worked out of the system, return the wheels to straight ahead, and leave the engine running for several more min.
Then road test...to the auto parts store and buy a Haynes repair manual. Best $16.00 bucks you can spend.