Not as an app exactly, but you should check out Holly Herndon and Mat Dryhurt’s suite of tools called “Holly Plus”:
https://holly.plus/
I’m pretty sure you can access their model somehow and even train your own voice using their “spawning” approach.
She did an awesome TED talk demonstrating this:
https://www.ted.com/talks/holly_herndon_what_if_you_could_si...
Here’s a cool example, using Dolly Parton’s song “Jolene”:
https://www.youtube.com/watch?v=kPAEMUzDxuo
I don’t think it’s quite at the level of consumer use yet, but I know they’re working on it. Definitely check it out.