My English is not so good.
My knife handle is't close. I'm not sure it normally or not. Sure i worry about rust inside.
If it comes like that new, send it back.
If it's old, that warping happens sometimes with non stabilized woods. The wood handle on my forgecraft warped at one end and pulled away from the tang. If the pins are holding and the handle is not loose, then it's nothing to worry about. I filled mine with bees wax.
if you decide to keep it fill the gap with enough epoxy and clamp it overnight. if you don't have a clamp use some heavy weight.
First off, send it back if you can, and you should be able to. But if that unfortunately is not an option:
I'm not sure I would clamp it, might separate again. I have successfully filed such gaps with epoxy. Once filled it is unlikely to separate more. Check first to see if you push it together and it stays, then you are "more" safe to open it again, epoxy and squeeze lightly back together.
Epoxy likes to have a minimum .005"/.125mm thickness for best strength. Squeeze to hard and you may squeeze out completely in some areas also, and wind up with less coverage. With metal involve which has had no treatment of the surface to roughen it, and handle material that might be in the same situation, the bond is going to be less than Ideal as it is.
I think it safest just to fill the gap as it is.
Can't you send them a pick?
If I had it to repair I'd:
clean it good - make sure there is no food, rust, etc. in the joint.
Then wash with acetone, then alcohol and let dry.
For pin point applications like this, or gluing wa handles on I make a 3" square of wax paper and mix my epoxy on that. Then I fold it up like a pastry bag and squeeze the epoxy in the handle all around and to the middle.
Then clamp, cleanup any squeeze out with a rag & some white vinegar.
Once it's set find a flat piece of steel and take a small hammer and peen the rivets tight.
You'll have a little clean up and sanding/polishing, but it should be right as rain afterwards. Good luck and just be mindful of "order of operations" and remember -
you can do it.