Try looking here:
https://www.serebii.net/games/hidden-power.shtml
Flame healer, is that your Bagon's IVs or is that their EVs?
There are two ways you can determine your IVs.
Firstly, use an IV Calculator. But then, it is not always accurate.
Secondly, it has to do something with online play I think. Set your Pokemon to Lv 100... But I don't know that.
Simply put, if you only want to know your Hidden Power's type, test it on every type of Pokemon.
Then by the descriptions of super effective, not very effective, no effect just normal damage, you'll eventually find out. Example: Test it on an Abra. If it's super effective, you'd know that the HP is either Bug, Dark or Ghost. Then test it on Ponyta. If it's not very effective, it's Bug then. And so on.
But then, you will not know the HP's Base Power.