Auto-record allows the helmet to record by default, whenever turned on with an SD card inserted.
You need to install the app and connect it to your helmet to activate Auto Record, but from then on the helmet will record whether you have the app running or not. Whenever your helmet is turned off or runs out of battery, it will stop recording and save the file.
If your "Auto-record" switch is greyed out, it is either because your helmet is not on and connected, or your helmet does not yet support Auto Record.
Auto-record was added to FE and MK1 in the firmware version 0.46.22 (the software that runs on the helmet), released in December 2020. If your helmet was assembled before then, you will need to update your helmet's firmware to enable it.
If you go to Settings > Helmet > Firmware update, you can see the version of the CPU firmware installed on your helmet. If it is earlier than version 46.22, Auto-record won't work. Please see the FAQ article on Firmware updating if you need assistance to update your helmet.