To fasten your seat belt:

Pull it out of the retractor and insert the metal tab (1) into the buckle (2). There will be an audible "click" when the tab locks into the buckle.
The seat belt automatically adjusts to the proper length after the lap belt portion is adjusted manually so that it fits snugly around your hips. If you lean forward in a slow, easy motion, the belt will extend and move with you. If there is a sudden stop or impact, the belt will lock into position. It will also lock if you try to lean forward too quickly.
NOTICE
If you are not able to smoothly pull enough of the seat belt out from the retractor, firmly pull the seat belt out and release it. After release, you will be able to pull the belt out smoothly.

WARNING
Improperly positioned seat belts may increase the risk of serious injury in an accident.Take the following precautions when adjusting the seat belt:
Height adjustment
You can adjust the height of the shoulder belt anchor to one of the four different positions for maximum comfort and safety.
The shoulder portion should be adjusted so it lies across your chest and midway over your shoulder nearest the door, not over your neck.

To adjust the height of the seat belt anchor, lower or raise the height adjuster into an appropriate position.
To raise the height adjuster, pull it up (1). To lower it, push it down (3) while pressing the height adjuster button (2).
Release the button to lock the anchor into position. Try sliding the height adjuster to make sure that it has locked into position.
To release your seat belt:

Press the release button (1) in the locking buckle.
When it is released, the belt should automatically draw back into the retractor. If this does not happen, check the belt to be sure it is not twisted, then try again.
Rear center seatbelt (3-point rear center seat belt)Hyundai Kona (OS) 2018-2026 Service Manual: Side Airbag (SAB) Module Description and operation
Description
The Side Airbags (SAB) are installed inside the front seat and protects the
driver and passenger from danger when side crash occurs. The SRSCM determines
deployment of side airbag by using Side Impact Sensor (SIS) signal.
...
Hyundai Kona (OS) 2018-2026 Owners Manual: Opening the tailgate
Make sure the vehicle is in P (Park) and set the parking brake.
Then do one of the following:
1. Unlock all doors with the Door Unlock button on your remote key or smart key.
Press the tailgate handle button and open the tailgate.
2. Press and hold the Tailgate Unlock button on the remote key or s ...