I have a nuget package in my project, and I am using one model from that package. Below

public class InOrderItemModel
{
    public InOrderItemModel();
    public string Description { get; set; }
    public int Quantity { get; set; }
    public decimal Price { get; set; }
}

In the above class I need to add few more properties so that I can populate and use it. I have to add below

public string OfferCode { get; set; }
public int ItemId { get; set; }
public decimal Price { get; set; }

I don't want to create a new class. Don't want to disturb existing value assignments and all. I just want to get the required properties so that I can add data and use it when required How can I do that ?