GitHub action self hosted retrieve `runs-on` field

Hi all,
We are running self-hosted runners in our AWS account using ECS. We created a Lambda function that runs a new runner every time someone pushes code and the check runs event has triggered making a webhook call to our API gateway endpoint.
We would like to create more than one cluster with different resources and runs runners based on the runs-on field value. I could not find this information in the docs, can someone point me in the right direction, please.