BB Boom IZZA Notice D'utilisation page 27

4.4. Adjust and use the harness
Loosen the harness
PRESS
Tighten the harness
PRESS
4.5. Adjust the enhanced child seat to different recline positions
The seat body of the enhanced child seat can be adjusted 4 different positions :
rearward facing position, position1,position2,position3.
The harness is slackened by pressing the
adjuster button of the central adjuster on
the front of the seat.
Press down the adjuster button as you grip
the two shoulder straps with your another
hand.
Pull the shoulder straps towards you to
loosen the harness.
Pull the shoulder straps upwards to remove
the slack from the lap sections of the
harness then pull the adjuster strap until the
harness is fully tightened.
The harness should be adjusted as tightly as
possible without causing discomfort to your
child.
A loose harness can be dangerous. Check
the harness adjuster and tighten each time
the child is placed in the seat.