It's ok if you already pressed the bushing into the lower control arm.
To press the pivot pin (shaft) into the bushing that's now in the LCA, all that you have to do is support the bushing from the back side by using a deep impact socket that fits the diameter of the bushing.
Your probably gonna be needing a third hand to support the socket in the LCA, and then using another of your hands to hold the LCA under the arm of the press, and then your other hand to pump the handle of the press.
Easy, peasy, once you figure it out, and do a set for the first time.
