BPI R3 does not boot anymore

Hello,

I have a brand new BPI R3 and while I was trying to install the latest snapshot of openwrt on the NAND, I accidentaly ran the reste to factory defaults in the SD Card swtich configuration.

Now my BPI does not show the Boot menu in serial connection mode.

Could you help me please ? I don’t know how to solve that. Thanks for your help.