new alarm remote, need help finding ecu please help

hey guys, just recently ordered an alarm remote for my 2004 toyota celica GT to replace my spare. Unfortunately I ordered the OEM one and found out i needed the Audiovox one. Luckily they sent me the one i needed (i hope) and instructions to install. The instructions tell me to find the the ECU (Engine Control Unit) programming button but i cant find it, any help would be great! thanks