You can't have a factory or DreamOS image in your box at the moment. Else you would have this option.
You can put the box into Flash mode by shutting down rhe box (Deep Standby)
After shutdown turn off the power with the switch on tha back.
Wait about 30 seconds and then follow this steps.
Turn on the power switch on the back and as soon as you done that.
Press and hold the front tuch button pressed ubtil you see in your lcd display a big ! sign
Now you can release the button and your box goes into flash mode.
IMPORTANT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Never press the go button for flashing without first uncheck the 2 boxes for backup and restore settings!!!!!!!
Make sure you do not backup an restore any setting!!!!!