Subaru BRZ 2018 Owner's Manual page 150

1-7. Safety information
Installing child restraints using a seatbelt (child restraint lock
function belt)
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Rear facing
STEP 1
STEP 2
STEP 3
148
Infant seat/convertible seat
Place the child restraint system
on the rear seat facing the rear
of the vehicle.
Run the seatbelt through the
child restraint system and insert
the plate into the buckle. Make
sure that the belt is not twisted.
Fully extend the shoulder belt
and allow it to retract to put it in
lock mode. In lock mode, the belt
cannot be extended.