Entity Framework: how to add an association, based on an existing property

Question

I'm using the database-first approach while setting my first steps in Entity Framework. In my SQL Server database I have two tables, Location and Area.

Both have an Id column and the Location table already has an AreadId property. I would like to use this property for creating a one-to-many association between both tables (many Location entries for one Area entry), so I have created the following in my EDMX diagram using the EDMX-designer:

In the automatically generated Location.cs file, it looks as follows:

public partial class Location
{
    ...
    public int AreaId { get; set; }
    ...
    public virtual Area Area { get; set; }
}

I would like to use the already existing property Location.AreaId as the foreign key. How can I do that, using EDMX-designer?

Please keep in mind that I can modify the EDMX diagram, but not the automatically generated Location.cs file.

Thanks in advance