The Syrus Lynx back cover doesn’t have screws it just snaps in so to open it, just lift one of the corners with a tiny screw or with your nail (the corner has a slot)
Once you remove the back cover, slide the sim card metal door to unlock it and open it by lifting it (Blue arrow in the picture below)
The metal door opens completely
Place the sim card (make sure to place it properly based on the cut corner position, yellowarrow in the picture below) with the metal part of the sim card facing the device and touching the metal pins of the sim card’s socket
Close the sim card metal door and slide back in the opposite direction to lock it (Red arrowin the picture below)
Put the Syrus Lynx cover back into the device until it snaps in again.