How to add simulator iPhone XS in Xcode 9.2 also iPhone XS max

In Xcode go to Window > Devices and Simulators Here click on the simulators and then click on '+' to add a desired device.

Update 2020

Open xcode simulator File > Open device > select your desired device.

Simple solution:

1. Open Xcode.
2. Select the "Window" menu.
3. Select "Devices and Simulators".
4. Select Simulators tab.
5. Click on the "+" icon at the left bottom.
6. Choose the desired device & preferred iOS.
7. Click "Create".
8. Enjoy :).

For those here with the same problem but for Xcode 10.x and need iOS 13 simulators (iPhone 11, for instance) do the following:

1. Install and open Xcode 11
2. Go to Xcode menu > Open Developer Tool > Simulator
3. On the Simulator app, go to Hardware menu > Device > iOS 13 to select and run your desired device
4. Now you can close Xcode 11, and open Xcode 10.x
5. You should see your i.e iPhone 11 simulator available in the Device List as the image: