Android App needs to be improvised

Android app that I have needs to be improvised for both, 1) GUI 2) Performance And some issues need to be fixed such as, 1) App not visible to some Android devices 2) Downloading of the video for offline viewing needs to be perfected. Currently there are issues such as download fails or during download page needs to be kept open or download progress is not accurate 3) Test questions to be automatically downloaded on device for offline practising. And offline data to be synchronised with website DB 4) Test functionality GUI to be improvised for ease of use 5) BigBlueButton training joining function to be added so user can join virtual training course from Android device or view recordings from their virtual devices 6) Course validity and expiry to be implemented so user can't access the product after certain date or certain attempts. Even when user disconnects internet after first download of content. Attempts and validity is checked locally and access stopped after expiry. Attempt data to be uploaded to website DB the moment user connects to internet. Please provide your fixed price quote.