2013 Toyota Sienna Owners Manual - Page 508

1-7. Safety information Child restraint systems with a top tether strap (third seat) STEP 1 Secure the child restraint system using the seat belt or LATCH anchors. Adjust the head restraint to the uppermost position. STEP 2 Latch the hook onto the anchor bracket and tighten the top tether strap. Make sure the top tether strap is securely latched. STEP 3 Adjust the head restraint to the downmost position.