Question: Most iOS version are downloaded, but all ios Version (iOS 8.x, iOS 9.x, etc doesn't appear in the dropdown on Xcode.  

How to reset this? (I know I can re-add manually using "Devices, Add", but i'm sure it's a way to just reset all, and have Xcode to offer redownload the sim.)

EDIT: The iOS I need to redownload, are the one that are ALREADY downloaded. – Franck 

[![enter image description here](https://i.stack.imgur.com/HSgpw.png)](https://i.stack.imgur.com/HSgpw.png)

[![enter image description here](https://i.stack.imgur.com/DQ40T.png)](https://i.stack.imgur.com/DQ40T.png)

Answer: 
I get my answer from the 'snapshot' git. (Fastlane)

> 
> reset\_simulators is removing all simulators and create new one only
>  for the latest iOS version. If you want to recreate simulators for
>  other versions you have to provide the list of the versions after the
>  --ios argument, e.g.
> 
> 
> snapshot reset\_simulators --ios 8.3,8.4,9.0,9.1
> 
> 
> 

Work perfectly!
In Xcode go to *Window > Devices* and see if you have duplicates in the list of devices there. 

You can delete devices here by selecting one and using the delete key. After deleting you will see the related download as not started in the *Downloads* window. Xcode will offer to re-download eventually or you can start the download manually.