To "soothe" or "calm" someone in Engpsh, you can say "calm down" or "relax." For example: "Calm down, everything is going to be okay." or "Relax, take a deep breath and try to calm yourself."

It's also possible to use more soothing or comforting phrases, such as "There, there" or "It's alright." For example: "There, there, it's going to be okay." or "It's alright, everything will work out in the end."

Remember that the most important thing is to be understanding and supportive, and to use a calming tone of voice.