In the help where everything else is; add an upgrade button. This simply needs to be a link to the latest version online.
If not in Help then how about another button in the About window?
With the Jet 2019 release (19.0.18268.1), a notification button is added to the Jet tab if the add-in version is less than the version of Jet Service Tier it is connected to. If not connected to a Jet Service Tier, then it checks for the version available for download.
Read more about it in the What's New or Release Notes articles.