Note: this feature is part of Homey Experiments. We cannot give support on experiments so use them at your own risk.
This experiment is only available for Homeys with built-in microphones. You can check which Homey model you have via More (...) --> Settings --> General --> Homey model. Read this article to find out which Homey models have built-in microphones.
After enabling this experiment you will be able to use the built-in microphones in Homey. You can read more about Homey in combination with speech in this category.