Acer AB460 F1 - Manual (Page 563)

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Use the "H" option to set hardware information by typing the character
H . This will display the hardware information that can be changed as
shown in.
4. To choose the boot from a fallback image, type the command:
rflag=1
5. Type Save to save the hardware information.
6. Type Exit to exit the hardware information menu.
7. Type J to boot the image. In this case it will boot from a fallback
image.
8. In case you wish to later move back to a normal image, repeat the
above the steps with one difference for step 4, where you should
use the command rflag=0
instead of rflag=1 to boot with a
normal firmware image.