Improve performance for known unlabelled test set
You are asking something different than standard machine learning. In standard machine learning, a test set is a dataset with labels that is evaluated a single time. The result of the test set evaluation is never used to change the model.
Another way to frame your question is - &quot;I have high quality unlabeled data that I would combine with my labeled data to create a model.&quot;
The answer to that question is semi-supervised learning.