The MachXO2 has a dual boot feature that works in an automatic mode. If the image loaded from the internal flash is found to have an issue (CRC error), or if the internal flash is erased, then the part will automatically try to load the golden image from the external SPI flash. The dual boot mode only supports this boot order; Internal flash, then external SPI flash.
To test the loading from the golden image you can erase the internal flash memory and then reboot the device by cycling the power on the system.
There is no I/O pin that can be used to force the device to boot from the external SPI flash when in dual boot mode. The external SPI flash will only be used if there is an error in the download from the internal flash memory or if the internal flash memory is erased.
The MachXO2 can also be configured to always boot from an external SPI flash in a single boot mode if desired and not use the internal flash memory.