Thanks for letting us know. How did you do this? Turkey baster method? What fluid is recommended?
maybe use a turkey baster to extract what you can from the reservoir, that or a handheld pump. But after that you pull the return hose to the pump/resv which allows the old fluid to be mechan' pumped into a can while simultaneously filling the reservoir with new PSF, front tires off ground and turning wheels back & forth. It requires somebody helping you, imperative the reservoir never runs dry if you are going to idle the engine -- just run a quart through it, re-attach the line after the chem is coming out clear for a bit. Any generic PSF will be OK. the owners manual has the GM-spec chems listed within if you want to be detailed about it.
for a real flush, you would dump the orig fluid, refill with SeaFoam Transtune and work that in thoroughly. Flush
that and then refill with PSF.