In the equalizer section, try the Mellow preset first, that's not bad for audiobooks. Usually we don't want too much treble for spoken word stuff.
1kHz and 2.5kHz are common human voice frequencies, 6.3kHz can also be harsh, turning these bands down would make the sound more mellow. I also like to bump up the bass on spoken word stuff. The Mellow preset has low bass (clear bass set at -3) so you can try adding more (clear bass +5 for instance).
If you want to change it, click on the gear at the bottom right corner of the panel, it'll show you the 5 bands and the clear bass slider. If you change anything you'll see the name turn into "Manual" and it'll be saved under "Manual" in the main screen.
I've never seen headphones work with outside apps because the app is basically controls that should've appeared as buttons on the headphone itself. (imagine that) Companies would argue it's only right that it's proprietary to them, no matter how crap it is :P
If you have a spare, throwaway phone, put the app on there for when you need to change settings. You can disable location in system settings and then allow location for the app, technically the app won't really get to know your location because the system has no location to provide.
If an app wants to foul this and spy on your location with location off, the app has to have Instagram-grade snooping, where if you use any web browser or google app, they will detect your location from that... But most apps are not assholes like that (yet) lol
I'm a bit older and I find this trend of headphones having apps really unfortunate. It's forced a lot of brands who are unsavvy to make bad software. And, do you guys remember Bose was caught selling user info from their first headphone app? (for the QC30)