Hi Thomas,
If you would like to get early access to the feature, then you should install update manually.
From this article,
https://docs.microsoft.com/en-us/dynamics365/marketing/whats-new-marketing#version-number
the version number of September early access update is 1.35.10065.2064, so the feature might be released in this version.
You could check current version of your marketing application in https://make.powerapps.com/,
Mine is 1.35.10065.1064, which is GA release, and the marketing configuration page said that my application is up to date.

However, the newer early access version mentioned by documentation is still not available for me.
In a word, as I said at the beginning, to get early access of features, we should update manually.
Or wait for general availability, by then all features will be updated automatically.
Regards,
Clofly