Thanks for the question. The Auto-Indexing feature for Serverless Instances is currently in private preview and is rolling out to customers over the next few weeks. Therefore, it is possible that your instance has not been enabled for it yet. We will add a “private preview” tag in our documentation to denote this.
In the first iteration, auto-indexing will be a UI only feature. I’d like to understand more about your use case and how you’d like to use it using terraform or an API call. Feel free to reply on this thread or direct message me.