How to change Push notification sound

Can anyone tell me how to use custom sound to push notification (Not local notification), currently i am using default sound for receiving notification but i want to change default sound to my other sound file.
thanks

this.http.post(‘https://fcm.googleapis.com/fcm/send’,
JSON.stringify({
notification: {
title: “Hello”,
body: " needs your help!",
sound: “default”, //want to change default to custom sound
click_action: “FCM_PLUGIN_ACTIVITY”
},