DatePicker format in SDK

Hi team, A datepicker field, normally looked like below in JSON, where the "pattern" field represents the format:

{
  "name": "",
  "type": "INPUT",
  "binding": null,
  "validation": {
    "errorMessage": "",
    "required": false,
    "enum": null,
    "maxLength": null,
    "errorCode": null,
    "minLength": null,
    "pattern": "YYYY-MM-dd"
  },
  "id": "O12oI48vdTs5",
  "subtype": "DATEPICKER",
  "page": 0,
  "extractAnchor": null,
  "formattedValue": "",
  "extract": false,
  "height": 37,
  "left": 301,
  "fontSize": null,
  "top": 261,
  "width": 165,
  "data": null,
  "value": null
}

However, we have difficulty adding the text format, with .Net SDK code. Could you help with this? Thanks!