Use the Allen key to remove each of the bolts securing the side panels to the foot board of the crib. The bolts go through the side panels into the back of the foot board and can be removed by turning counter-clockwise.
Align the bottom of the toddler rail to the mattress support system. When this is lined up, the holes on the guardrail should also line up to the holes in the ends of the side panels. Insert one Allen bolt through each hole on the guardrail into the side panels. Secure this part by inserting the Allen key into each bolt and turning clockwise until tightened.
Check all Allen bolts securing the headboard to the side panels and the mattress support assembly. If any of the bolts are loose, tighten them by turning clockwise with the Allen key.