Check the indoor unit for a manual power button
Open the front panel of the AC
Look for an emergency or auto on/off button near the filters or control board
Press the button once to turn the AC on
Press it again to cycle modes if supported
Use the wall switch or circuit breaker to power the unit if it is already set to auto-start
Install a universal AC remote if the unit has no manual button
Use a smartphone IR blaster app if your phone supports infrared
Replace the remote batteries if the remote is missing but available later
Contact the AC brand service center for a compatible replacement remote