Not sure if you can just wait for this to cool or not, possibly or might need to reset the plane.
Go to your right hand FMC, hit PMDG setup, then aircraft, then failures and you should see the brake failure highlighted. From memory there will be options to clear it but I can’t remember if you might still need to restart the plane or not. Also when you are in that area it’s worth looking through the options pages 1-4 as it gives options to have service based failures turned on or off or random. Lots of options overall for this plane, take your time, explore it. it’s an excellent aircraft. I’m not an expert by any means but hope this helps a bit.
Rob