Toyota 2015 Prius Owner's Manual page 199

1-8. Safety information
STEP 2
Outside only: Do the following.
STEP 3
Foldable type
Non-foldable type
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PRIUS_OM_OM47A17U_DVD_(U)
Open the anchor bracket cover,
latch the hook onto the anchor
bracket and tighten the top tether
strap.
Make sure the top tether strap is
securely latched.
Adjust the head restraint to the
downmost position.
Install the head restraint.