const firestore = firebase.firestore();
// get the data from 'name@xxx.com'
firestore.collection("users").doc("name@xxx.com").get().then(function (doc) {
if (doc && doc.exists) {
var data = doc.data();
// saves the data to 'name'
firestore.collection("users").doc("name").set(data).then({
// deletes the old document
firestore.collection("users").doc("name@xxx.com").delete();
});
}
});