How do I reset my 2007 chevy avalanche computer?

On the 2007 Chevrolet Avalanche, there's no "soft" way to reset the engine control module (ECM), which is most likely what You mean by the "computer". You'll need to perform a "hard" reset, by disconnecting the negative battery cable. Let it sit for at least 15 minutes, with the headlight switch on. Once You reconnect the negative terminal, power will be restored and the ECM should be reset. Some technicians report another method of total power discharge. The reason You turn the headlight switch to ON and wait so long is because an internal capacitor holds some charge, even with the battery disconnected. These technicians say that removing both terminals and touching them together for 5-10 seconds will expedite the process, though others disagree. If You're not in a rush, You should likely just use the first method.