Plug the phone into a charger
Use the volume buttons if the phone supports power-on by key combo
Connect the phone to a computer or USB power source
Remove and reinsert the battery if the phone has a removable battery
Use the scheduled power-on feature if enabled
Open the phone with a USB OTG cable and accessory if supported
Use a wake-on-charge or auto-boot feature if available
Ask a repair technician to replace or repair the power button