IPhone - Customizable reality checks sound ?

Hi,

I just tested some free IOS11 applications to do reality checks (random reminders).
But I really regret that it is not possible to replace the sound with one of my AAC/MP3.

Do you know a way to do that ?
(commercial apps are welcome too)

Thanks you in advance.
PS: i can’t change the sound notifications per apps in my IPhone settings