Hi Rocky - Aria is an Elevenlabs voice for the pre-written scripts. If you add a custom caption from the 'Choose Script's dialogue, once the custom caption is written and selected, you'll be able to select a voice dialogue. This is where you can choose the custom Elevenlabs/Fish Audio voices and keys.
I hope this helps! Thank you for supporting the program and let me know if you have any more questions.
-Rem