Please watch the following Dell Support video on YouTube which includes additional support information.    Start by using Revo Uninstaller Free to remove SupportAssist and its Advanced Scan to remove any remaining multiple files, folders, and/or Registry entries.  Please visit the Dell SupportAssist for PCs forum. SupportAssist for PCs - Dell Community 
SupportAssist Installation failed, what can I do?
"DS: SupportAssist Installation failed, what can I do?"