SA installs silently in the background, so its possible that it is installed. Open Windows store and go to Library - Apps and look for supportassist in the list: 

I started AssistSupport and received a message "This is taking longer than expected. We recommend restarting your PC and trying again." I did this several times just got the same message.  I decided to delete the AssistSupport from the list of Apps in the Windows icon - Settings - Apps, and the app was not listed in the Apps list thereafter.  I downloaded the latest version of the Dell AssistSupport installation app.  When I start the installation, the AssistSupport screen appeared, but after a few seconds messaged that the app was already installed.  The AssistSupport app still was missing from the Settings/Apps list, leaving me no way to start it.

@sgmichael​ BTW, I looked at the Microsoft Store app and there were four Dell apps there, but not the Dell AssistSupport app.   The Windows - Settings - Apps lists it, but doesn't offer a way to open it (just "Modify" and "Uninstall"