How to retrieve the variable from API call start data

I am using Nintex for office 365 to create component workflow and use HTTP API call to trigger the workflow. The data below will be transferred to workflow when we implement the API call, how can we get the workflow variable from below instance start data? Thanks.

{
    "tenantId": {
        "entityType": "TENANT",
        "id": "464a6ca0-6fe4-11e9-a022-17093da0953d"
    },
    "type": "High Temp Alarm",
    "originator": {
        "entityType": "DEVICE",
        "id": "a75bdac0-4634-11ea-b164-1ba777a71e90"
    },
    "severity": "CRITICAL",
    "status": "ACTIVE_UNACK",
    "startTs": 1581674889099,
    "endTs": 1581674889099,
    "ackTs": 0,
    "clearTs": 0,
    "details": {},
    "propagate": true,
    "id": {
        "entityType": "ALARM",
        "id": "e6a7b3d0-4f11-11ea-b164-1ba777a71e90"
    },
    "createdTime": 1581674889101,
    "name": "High Temp Alarm"
}

As you can see, all data are not under the class "startData", how can we retrieve above data and then configure it as variable? Thank you.