kindly go up to both of the customers and ask them what’s wrong. Then let one of them say their side of the story first, then ask the next to speak their side of the story when the other is finished. Then i would see who’s in the wrong, but also offer the customer that is not wearing a mask to wear one, then if they decide to not listen and just brush aside of them not wearing a mask, i would then start stating how dangerous and serious this pandemic is and how not only this customer is in danger, but many people as well.