Modify on Backend ASP .NET

We can to understanding that an modifying is needed for our backend in one of our data models. The app core future is to create a post of used car for sale. the post creation ask the user to input Brand, Model, Body Type, Transmision Type, etc.. but we are missing one more filed that we would like to store the cars in our backend with is that for every brand there is many models and sometimes for a model there is submodel for example: Brand: BWM Model: M Submodel: M5 or Brand: Mercedes-Benz Model: C Class Submodel: C260 so we need to change the structure of car model and it relationships Also, we have a feature that needs better implementation in the backend which is: User can search for cars in our search engine, and they can request to "Notify me if similar with similar posts" so if the user clicked on "Notify me if similar with similar posts" the app should save the current searching criteria for that user and would check for upcoming posts in future that match the user search filter. if posts/post is posted in future, the user should get a push notification to inform him/her about that/those new posts that match his/her saved search filter that they did a while ago