I don't believe there's an app that can do it without root. It's best to just follow the instructions in some of the articles that have been posted. I enabled adoptable storage and while it's cool, the phone stops displaying storage space correctly, and burst mode no longer works in the camera. If you can put up with those things though, go for it
In a lot of instances, this moves very little from internal storage but adoptive storage allows the ext SD card to be treated as internal storage which is fine unless the card goes bad or gets stolen.