[Q] Onda V711s tablet brick firmware

Hey,

I just got the v711s tablet directly from china and I tried to flash it with a new firmware but I didn't took the good one. Now the touch screen doesn't work and I'm unable to reflash it to an other firmware.
Also the boot manager is not responsive so no chance on this side (also I don't have volume button on the tablet).

You guys have any idea what should be my next step ?
Is a hard reset via SD card available ? Is there a way to get boot manager working ?

Thanks !