There are 2 screws that you need to remove on the tail lamp. They may have a cover over the screws, remove the covers and remove the screws. The tail lamp now just pulls off, it may be hard to get the tail lamp off but it just pulls off after the screws are removed, When you get the tail lamp off, you can get to the bulbs.
Tail Lamp Replacement (Enclave)
Open the lift gate in order to access the tail lamp access hinged hole covers.
Tail Lamp Access Hinged Hole Cover (Qty: 2)
Use a small flat bladed tool at the topside of the covers in order to release and open the hinged covers.
Tail Lamp Screw (Qty: 2)
Caution: Refer to Fastener Caution in the Preface section.
Tighten3 N·m (27 lb in)
Tail Lamp Assembly
Tail Lamp Filler Panel Nuts
TipInspect the filler panel nuts, replace if damaged.