With the release of Windows 1809 and LTSB 2019 Microsoft has changed how you install Remote Server Administration Tools this can be difficult at first but over all is simple.
To install RSAT on 1809 you will need an internet connection at this time and to install RSAT on LTSB 2019 you will need to download the LTSB 2019 feature ISOs from your volume licensing site
Open PowerShell as an administrator
Then run the following command
This will download and instal the needed files to install RAST then install them for you
If you are installing RSAT on LTSB 2019 then you will first mount the feature pack ISO then run the following command