Either use the Server Manager and click on Manage -> Add Roles and Features.
Or search for “Turn Windows Features on or off”.
A new window opens as shown below.
Select Role-based or feature-based installation and click Next >.
Select the Server you want the features to be installed on and click Next >.
Select Web Server (IIS). A new window is shown.
Click Add Features without changing anything and click Next >.
Feature configuration can be skipped, click Next > twice to get to the Role Services.
Make sure to check WebSocket Protocol. Leave all other options untouched. Click Next > and Install.