How do you calm someone down?

My boyfriend (long distance relationship) was raging on ft earlier because he kept dying in some game and i was just stuck on what to say. i told him to take a break n he just mimiced me and told me that he has nothing else to do. he kept talking ab how unlucky he's been and he kept saying fml. im his girlfriend and feel like i should be doing something but like what? he won't come off it and all his other games are 'trash'. how am i meant to make him chill? its bugging me cos I don't know what to do to help or how to get him to relax or even what to say to him?
How do you calm someone down?
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