Email your log files from Documents\Zwift\Logs to support@zwift.com with a description of your error (ie “installer crashes every time”) and it’ll get into our bug system properly. Specifying mac or PC helps too in the ticket.
I had issues with the initial installation and with some of the updates. Kept rebooting and trying and it finally worked. Another time, I used Explorer to navigate to the directory where Zwift was installed (C;\Program Files (X86)\Zwift) and then directly clicked on the ZwiftLauncher.exe file. that also worked.