This feature is not supported now. The official document doesn't mention the specific mechanism of ordering for agents in Call Queues. According to the experience and users' feedback, we could conclude that the serial routing is based on the alphabetical order.
Meanwhile, I found a feature request about this feature here. You could vote for it and add your comments.
Microsoft will always focus on customer’s feedback and experience. Some new features would be added to the services based on customers' feedback in the future, and your good ideas will be very helpful for them to improve the service.
Your time, understanding and cooperation will be highly appreciated.
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