Lexus ES300 Owner's Manual page 157

2. Fully extend the shoulder belt to put it in the lock mode.
When the belt is then retracted slightly, it cannot be extended.
To hold the convertible seat securely, make sure the belt is in
the lock mode before letting the belt retract.
COMFORT ADJUSTMENT
3. While pressing the convertible seat firmly against the seat
cushion and seatback, let the shoulder belt retract as far as it
will go to hold the convertible seat securely.
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