Hey @PCHH, this can be done easily with the inbuilt XML parser. Since SOAP responses are XML, you can proceed as follows:
let response = pm.response.text(), // this provides the response body as text. In this case, XML
body = xml2Json(response); // this converts XML to JSON
console.log(body); // this aids understanding
// now that body contains the JSON equivalent of the SOAP response, required keys can be fetched and saved as follows
pm.environment.set('id', body.<required property name>); // <required property name> will have to be replaced with the actual path of the ID in the nested JSON structure