It's easy.
Lift the front of the truck and put it on stands so that the wheels can be turned without wearing the tires.
Disconnect the fluid return hose and put it into a catch vessel. It should be the top of the two hoses going into the power steering reservoir.
Turn the key to run/on but don't start it. Turn the wheel all the way to one side then back to center. Check the fluid level. Turn the wheel all the way to the other side then back to center. Check the fluid level.
Add fluid to the reservoir any time it gets low. Repeat the steps above until fresh fluid is getting all the way to the collection vessel. When you're done just reattach the hose and clean up any spills.
The whole thing will take less than half an hour.