Setting User-defined property on UI

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1

I am trying to set a user-define property on a postman requests based on here

Any property name in the new format that starts with an underscore character will be treated as a user-defined property (except _postman as a reserved one).

Let’s say an example:

{
	"info": {
		"_postman_id": "f4800b0b-b86f-43c4-90e4-602f74c0e317",
		"name": "Hello",
		"schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
	},
	"item": [
		{
			"name": "New Request",
			"_myCustomProperty" : "property_value",
			"event": [
				{
					"listen": "test",
					"script": {
						"exec": [
							"pm.test(\"Status code is 200\", function () {",
							"    pm.response.to.have.status(200);",
							"});"
						],
						"type": "text/javascript"
					}
				}
			],
			"request": {
				"method": "GET",
				"header": [],
				"url": {
					"raw": "https://postman.com",
					"protocol": "https",
					"host": [
						"postman",
						"com"
					]
				}
			},
			"response": []
		}
	]
}

Where do I set this _myCustomProperty on Postman app on Mac? I don’t see any options anywhere else in Params, Authorization, Headers, etc. Is user-defined property supported on Postman app, and if so where do I set them?