How to Enable Android Download Manager

Please edit my answer if is not valid

Check if download manager is available:

   int state = this.getPackageManager().getApplicationEnabledSetting("com.android.providers.downloads");

if(state==PackageManager.COMPONENT_ENABLED_STATE_DISABLED||
state==PackageManager.COMPONENT_ENABLED_STATE_DISABLED_USER
||state==PackageManager.COMPONENT_ENABLED_STATE_DISABLED_UNTIL_USED){

// Cannot download using download manager
}

            else {
                request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName);
                request.setDescription(fileName);   
                manager.enqueue(request); 
            }

And the solution for trying to enable download manager is:

packageName = "com.android.providers.downloads"

try {
    //Open the specific App Info page:
    Intent intent = new Intent(android.provider.Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
    intent.setData(Uri.parse("package:" + packageName));
    startActivity(intent);

} catch ( ActivityNotFoundException e ) {
    //e.printStackTrace();

    //Open the generic Apps page:
    Intent intent = new Intent(android.provider.Settings.ACTION_MANAGE_APPLICATIONS_SETTINGS);
    startActivity(intent);

}