Back to Original Firmware from Xiaomi 3g Router?

Hardware Questions and Recommendations
1

I successfully flashed openwrt on the MiR3G.
Now I want to go back to the original firmware. I already have a USB to TTL adapter and can see the output in Putty. However, I can't interrupt the boot process to select option 2. Or is there an easier way to go back to the original firmware?

2

no gadget soldering needed.