WARNING: do NOT attempt to do this unless there is an actual emergency; it is hazardous for you to turn the gas valve back on, and the gas company may charge you a significant amount for them to do it safely.
How to Shut Off Your Natural Gas in an Emergency. Learn hot to locate and shut off your natural gas meter in case of an emergency.
https://www.socalgas.com/stay-safe/emergency-information/shut-off-natural-gas