Ok. The harmonic balancer is the main engine pulley. You will need to remove the belt, remove the large bolt and use a harmonic balancer puller to remove the pulley.
Here are the GM instructions.
Crankshaft Balancer Replacement Removal Procedure
Important: Do not attempt to separate the pulley from the balancer hub. The balancer is serviced as an assembly.
Notice: This bolt is designed to permanently stretch when tightened, and therefore MUST be replaced anytime it is removed. The correct part number fastener must be used to replace this type of fastener. Do not use a bolt that is stronger in this application. If the correct bolt is not used, the parts will not be tightened correctly. The system or the components may be damaged.
Tighten Tighten the bolt to 150 N·m (111 lb ft). Use a torque angle meter in order to rotate the bolt an additional 76 degrees.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.
Ok. First, *it happens. You should not have to replace the balancer unless you see damage. Here are the instructions for removing the tensioner.