How to autoStart?

Hi, I bought a bpi-r2 and tried to boot from an image with a 12V 2A power supply. When pressing the boot button the 3 LED light up. When releasing the boot button the LEDs turn off and starting with EMMC.

But I Want to autostart When I Plug in power supply。how to do?

There are existing some threads about this and the info in my wiki

https://www.fw-web.de/dokuwiki/doku.php?id=en:bpi-r2:hardware