May not be helpful but that smooth part of the egr pipe slides into the egr valve a good bit before the collar is even close to threading on. You have a few options for getting it back together but you definitely want the egr pipe slid onto the egr valve before you start tightening the nuts that hold the egr valve on.
You may even want to pull one or move of the studs out of the intake manifold to make moving the egr valve easier so that you can get the pipe into the valve and perhaps the collar on a turn or two before you then install the studs and nuts and tighten things down. In the event that you bent the egr pipe out of the way somehow during removal or install of the egr valve you may also need to work against that bend more than otherwise, etc.
One word of caution is that if you pull one or more studs out to help you get the pipe back into the valve be very wary of cross threading them on their way back into the aluminum intake.
Good luck.
