Toyota 2015 Prius Owner's Manual page 197

1-8. Safety information
Removing a child restraint installed with a seat belt
Child restraint systems with a top tether strap
Secure the child restraint system using a seat belt or the
STEP 1
LATCH anchors, and do the following.
Foldable type outside seats
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Press the buckle release button
and fully retract the seat belt.
Adjust the head restraint to the
upmost position.