stsClient issue with private notebook

Customer was using PySpark SDK with a notebook without public internet access, they configured the notebook in a way to connect to their regional sts endpoint not the global one, when initializing the KMeansSageMakerEstimator, the stsClient is default to the global one which is causing a time out error. How could they modify the stsClient so they can connect to their regional sts endpoint instead?

Start by tracing KMeansSageMakerEstimator initialization and inspecting where its stsClient is selected. Reproduce the private-notebook timeout with a regional STS endpoint, then determine how regional endpoint configuration can be honored and verify that initialization connects to the configured endpoint.

Written by the indexing model from the issue text.