Hey,
This was a bug recently discovered, we are working on a fix.
In the meantime could you try this workaround:
1.) Goto your launcher install directory, then drill down into Launcher\Engine\Binaries\Win64
2.) There you should find UnrealVersionSelector.exe. Right click and create a shortcut for this.
3.) Right click on the shortcut and hit Properties.
4.) On the shortcut tab of the properties window you should see a “Target” field. Go to the very end of this add a space at the end if there isn’t one, then add /fileassociations
5.) Click ok. The window should close.
6.) Right click on the shortcut again and select Run as administrator. A dialog will likely pop up asking for permission. If so click yes.
Let me know if this sorts you out.