Expired certificate on high Sierra installer. App Store only shows “open” since already downloaded. How can I redownload a fresh copy of high Sierra or any expired installer?

Getting message that the installer is damaged bight on reinstall of Sierra and when trying to upgrade to High Sierra. Researching it looks like the certificates have expired as the installers were downloaded quite awhile ago. When attempting to re download through the App Store the only option I have is to “open” and I’m assuming it’s because the installer is already downloaded.

question how do I download a fresh copy of an older installer that was previously downloaded?