See owner manual,( only have Compass manual from online, but should be the same) Seat Belts, in Section 2, around page 45.
"To disengage the mini latch from the mini buckle for
storage, insert the regular latch plate into the black
button on the top of the mini buckle. The belt will
automatically retract to its stowed position."
Its very easy, but be careful when the belt retracts not to let it go and hit the window.