Same problem I had. Fixed by doing the following; First make sure that windows is up to date with the latest updates. There is a new update for SA (version 3.3.3). So uninstall your current version and run CCleaner to fix registry errors and temp files. Restart your pc and download SA installer from here: [URL] Run it as administrator and let it do is thing.  
After installing Windows 10 Update 1903, I also could not run SupportAssist. I have tried all the steps in the solution, but the installer always hangs, with this message in the Application Event Log: Product: Dell SupportAssist -- Error 27555. Error attempting to apply permissions to object 'MACHINE\SOFTWARE\DELL\SupportAssistAgent'. System error: The system cannot find the file specified.(-2147024894) I'm a software engineer with computer expertise so I can get more information if needed. Thanks!  
Re: Installation of SupportAssist does not end