Hello my name is XXXXX XXXXX X will be more than happy to assist you.
Is it a replacement remote or do you need to resynchronize a remote that has been programed to the vehicle before?
To reprogram a replacement remote it will require the GM scanner or a scanner that has the reprogram function.
Here are the instructions from GM
All transmitters which are to be recognized by the remote control door lock receiver (RCDLR) must be programmed in a single programming sequence. If the system is placed in program mode, all previously programmed transmitters will be erased upon the receipt of the programming signal from the first transmitter. Up to four transmitters may be programmed. Do not operate or program the transmitters in the vicinity of other vehicles that are in the keyless entry program mode. This prevents the programming of the transmitters to the incorrect vehicle. The order in which the transmitters are programmed is important. The first transmitter programmed will be transmitter #1, and the second transmitter programmed will be transmitter #2. The number on the transmitters are for reference only: #2 can be programmed as #1, or vice versa. Additional unnumbered transmitters are also available. Use care to program the transmitters correctly.
The scan tool must stay connected until all of the transmitters are programmed.