That's a good question! It's definitely very rare that a birth name is entirely necessary to use in conversation, but an occasional situation comes up where I'm talking to an old friend about someone who's since transitioned and I need to use a deadname to let them know who I'm talking about. Generally I say something like "so I ran into Denise, you knew her as Brett back in the day, etc etc etc" and just use Denise from there on. If the person I'm talking to isn't caught too off guard by that, it's a very smooth and natural way to handle that as a matter of circumstance and move on to using the preferred name quickly.