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: 
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.
Click here to restart download ...
[![enter image description here](https://i.stack.imgur.com/d1He3.png)](https://i.stack.imgur.com/d1He3.png)

But if you really want to re-download, you can just delete the simulators and Xcode will offer to re-download.  

Go to `/Library/Developer/CoreSimulator/Profiles/Runtimes` and delete the files/bundles there