How to get specific inputs to Query Custom Objects

I am following along https://developers.marketo.com/rest-api/lead-database/custom-objects/#query and I the article doesn't explain how the unique identifiers for custom objects are acquired. Is it expected to scrape ID's for these custom objects from the Web GUI? If so that is a terrible option.

For example, from the docs:

POST /rest/v1/customobjects/{name}.json?_method=GET

Body

{

"filterType":"dedupeFields",

"fields":[

"marketoGuid",

"Bedrooms",

"yearBuilt"

],

"input":[

{

"mlsNum":"1962352",

"houseOwnerId":"42645756"

},

{

"mlsNum":"2962352",

"houseOwnerId":"52645756"

},

{

"mlsNum":"3962352",

"houseOwnerId":"62645756"

}

]

}

How are the"mIsNum" and "houseOwnerId" input identifiers acquired? What api call enabled these numbers to be retrieved? Specifically I am referring to the "1962352" value of "mlsNum":"1962352" and "42645756" of "houseOwnerId":"42645756".

Any help would be greatly appreciated!