Hi there Hugues 
This is strange!
From what i understand you have downloaded and installed Datasmith already.
If you have installed Unreal for the first time and your Unreal Studio Subscription is active.
You should be good to go.
Since its not the case,
You may want to double check in your launcher.
Make sure your Unreal Studio subscription is set to Active.
Also check in case the plugin needs to be updated:
If everything else fails…
You could always try removing the plugin (in case it did not install correctly)
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“small”,“data-tempid”:“temp_140095_1528917623693_149”}[/ATTACH]
https://forums.unrealengine.com/core/image/gif;base64
Install to engine again.
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“small”,“data-tempid”:“temp_140096_1528917637644_252”}[/ATTACH]
https://forums.unrealengine.com/core/image/gif;base64
If that did not fix your problem, we will need to investigate more.
Let me know
cheers
MC