List all Server Roles to see what's installed

Returns a fully expanded list of all features and subfeatures available on your server, as well as identifying which features are installed.

Open CMD prompt as administrator
run Powershell
run Import-Module ServerManager
run Get-WindowsFeature

Install Server Feature

Using the feature name from the output from above you can install a feature. If you wanted to add RSAT, you'd run

run Add-WindowsFeature RSAT