Select and open a file

Hi all!
In an ios app, I need to read a text file (in my case a csv one), and I need the user can navigate in the icloud or phone folders. In other apps (for example I use a digital signature app) the user is able to navigate in the folder system and choose a document, to process it.
I really don’t know how approach this. I have activated filesharing and icloud in the capabilities but folderitem.showopenfiledialog is unavailable in ios apps. With specialfolder I can access to a specific file, but I can’t give to the user the choice.

Any suggestion?

Thanks a lot!