To my knowledge, it is installed by default.

My apologies if I am not of much help, just trying to help you with my experience in debricking the router via uboot.

To make sure, are you sure you were pressing the reset button before powering on the router? Keep holding the reset button as you press the power button. If you don’t have a power button, hold the reset button before plugging in the router to the power source.

If you are already doing that correctly and still not working, sorry I have no idea what could be the issue.