Open a terminal and issue one of the following commands:
To shutdown and then erase / factory reset the Simulator clones – which doesn’t need an Xcode restart:
xcrun simctl --set testing shutdown all
xcrun simctl --set testing erase all
To delete / remove all the Simulator clones – remember to restart Xcode after doing this:
xcrun simctl --set testing delete all
If you want to list all the currently available ones:
xcrun simctl --set testing list devices