In the area between the river with the pipe, the new tree test location, the rozital ship part and most importantly UNIFORM. There is a pit with the plushy and a donut (donut helps you get unstuck).
Viewing post in Argemia plush toy locations.
Yea the round metal ship part. It looks like a puzzle imo, but you'll eventually see what it does. If you get a pink crystal looking signal and processed it, you should immediately head there, but you might already know about this...
Anyways, once you are at that ship part, you just gotta go to the river north from there towards the restricted area. Don't slide downhill towards the fence. I'm sure you will find it immediately, you got this.