I am not familiar with this app but IOS apps kinda work "backwards" compared to how Macs and PCs works. In other words you can't open a file that then opens in the app of your choice.
In IOS you can only operate on a file if the app allows it. You can only open (or save) a file on IOS if the app is designed to do so. So your app needs the option to save the .wav files in Dropbox or Google Drive. If it can't you are out of luck.
Often that will show up under the sharing button (box with an arrow pointed up) tap on that button and select what app to open it with. If it allows saving to Dropbox (or whatever...) you would have the option of sharing it with Dropbox.
It's an odd way of working with files if you come from a Mac or PC background but has it's own logic and makes sense once you understand the workflow.