Help please

That jet drops down that long tube.  It'll be visible when you look at the other side. 
 
The rubber seal end goes in first.  That somewhat holds the seal in your NIKKI carb. 
 
If you have something like a very thin, straight, dental pick put the jet on the tip of the pick.
Then hold the main white plastic part and slip it down over the jet.  Gently push it in till the rubber
o-ring seats..
 
You can also drop, then jiggle the jet till it's the correct direction in the hole and again, gently seat it.
 
Also, use just a touch of di-electric grease on the little o-ring (already installed, in your pic).  
The grease helps it to slip in easily with the aluminum carb body..
 
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