How can I call mutation in GraphQL playground?

My schema looks like this within the yellow coloured square in the image below

And the code on the left side doesn't really work. How can I call this in GraphQL playground?

Appreciate your answer in advance!

1. you can do input QUERY VARIABLES like

{ 
 "input": {
    "scheduleId: "123",
    "reason": "123"
 }
}

2. also you can input variables to directly

mutation {
 cancelScheduleByAdmin(input: {
    "scheduleId": "123",
    "reason": "123"
 }) {
   ...
 }
}