The intake tube hole has a groove in it. There is also a raised area on the end of the metal tube. The raised area on the tube should snap into the groove in the intake tube.
The way the metal tube was intended to be installed utilized a metal bracket that had to be bolted to the engine. This makes it very difficult to remove the intake tube. I have loosened the bolt and taken the slotted bracket out from behind the bolt, then tightened the bolt, or just bent the bracket so it doesn't fit behind the bolt. If you snap the tube into the valve cover and into the intake tube, it's not going to come out on its own.