I finally got this to work for me.
First, my goal was to switch from an FB log in to a password log in - because FB is blocked from my work computer and so I wasn't able to book any work travel using this method. My goal was not to remove FB entirely, just simply remove it from being the only log in option, so this system may not work for you if you are hoping to disconnect from fb entirely.
1) The AirBnb help forum says that to remove this log in system, you need to log out and then go through the "forgot password" chain and then the issue would be resolved. However, sitting here on my work computer I don't even see that option. The only option I am given is to sign in through facebook. No forgot password link.
1A) I logged onto my phone browser, and checked the desktop browser option so it didn't default to mobile. I logged out, got back into the sign in screen, and for some reason on this view the "forgot password" option was there. I did all of that and it worked! I now had a password.
1B) The above worked fine for my phone and for my mobile app. So I go to the desktop, the whole reason I'm even doing this, and IT STILL WANTS ME TO LOG IN TO FB. I was about to pull my hair out. So I click the option "Sign into another account" ....that is where you are able to just straight up put in your email and your new password. Its basically hidden!
so, tldr;: if you have done the forgot password chain and now have an actual password to use, but still aren't seeing an option to *use* it - check to see if there is a "sign into another account" option and put the email and password in there.