Create item with UID in firebase

I’m trying to create multiple items in the firebase list using user’s UID as we can in image bellow

this is my method to create items

  formCreate() {
        .then(() => { 

and my service I have this code to save item in list

  save(product: Product) {
    return new Promise((resolve) => {
          .then(() => resolve());

in this way the method is replacing the item to another item and not saving multiple items, how to resolve it’s ?
I realized that “set” update item and not save…