turtatical
Did you type your E-Mail address correctly? You might mis-spell it or you made a mistake. Also, some mail providers mark some mails as spam, so check your spam/trash too.
If steps I have listed above didn't solve your issue, re-create your forum, if you can (eg. if it didn't already create it). Use this step only when you are creating your forum. I assume you are trying to create it and you are not trying to send password reset mail for already exising user. There might be a "black hole" in some packets, like how I call it - or, in human language, when you tried to create your forum (which I assume that this is the thing you was trying to do) there might be a lag, small server outage or something like that. Therefore, an error followed (the "black hole") which ate all the tasks required for creating your forum (this is why I call errors "black holes" sometimes, because they tend to break the entire thing, if you don't have setup your error handler properly).
In another human language, even more simply, the forum creation process was not finished, therefore your admin password was not sent. That means if there is no data and server thinks that the forum does not exist, you might be able to run the task again.
Another possibility might be that FreeFlarum's mail service had some issues at the moment when you was creating the forum. Or something else has a problem.
I'm just trying to list all the possibilities here, so don't laugh at me. I might be wrong, because I'm not really a PhP or mail service developer (I can handle HTML, CSS and a bit of JavaScript. And GML. And Microsoft Paint... . . . )
Lastly, you can leave a message here once again so we can fix the issue. Be sure to provide any more information that will help us to catch your issue and give it a long vacation 🙂