From version 2.2 you are able to Edit deal details in mobile apps. To use and access edit deal option, click on "+" icon on the right side of the deal and select option Edit deal from the list:
The screen with deal details will load where you can make needed changes and when you are done just press "Save" in top right corner for them to apply.
IMPORTANT NOTE: Contact information are not editable. You are able to use trash can icon to remove contact completely from the deal and use add contact icon in header to replace them with another contact or just add more contacts to a deal. Still, individual contact records - First Name, Last Name, Mobil Phone, Email - will not save changes.