The WDT in PSoC 4 device is not expected to work in brown-out region.
Please note that the minimum voltage input required to expect the PSoC to work properly is 1.8 volts on VDDD/VDDA/VDDIO
The power to the WDT is supplied by Deep sleep regulator. In case of brown-out the deep sleep regulator will not get enough power to run the WDT.
.So there is no software which can bring the device out of brownout.