The r7800 "debricking" instructions using TFTP and a "factory" image are here.
I have a close cousin to the r7800, based on my own experience and the experience of others that have posted about the r7800 in these forums, these devices are very forgiving. A TFTP flash of a factory image should be a complete reset. It's unlikely you've lost your wifi due to flashing images.
That said, you shouldn't need this and just issuing firstboot from the cli (as the user above suggested) should get you back to the starting point. It may help others who could help you to know the community build you've loaded as well as posting the output of the additional commands suggested above.
Lastly, this community build is popular (read safe, works well, and a good place to start) for the r7800. Read the first post to get started.
HTH