How to config worker and .bbtravis.yml to make different repo use different worker?

I deploy a master, several workers, but our repo contains android and iOS. How to config to make android repo use android worker, iOS repo use iOS worker?

Start by reading the repository's worker configuration and the .bbtravis.yml entry point, then trace how a repository selects a worker. Document the configuration needed for Android and iOS repositories to use different workers, and verify that the instructions cover the stated master-and-several-workers setup.

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