C#: Alternative Method to Static Objects

So I'm working on a project and have hit a logic roadblock in my design of it.

Currently I have several forms, and classes. I have one form MainForm handles the main window of my program. Inside this class, I have a static ArrayList of type "Room".

    public partial class MainForm : Form
    {
        public static ArrayList rooms = new ArrayList();
        ...
    }

On load, MainForm will read in a list of items from a text file, and create "Room" objects and store them in an arraylist.

        public void loadSettings()
        {
            string path = System.IO.Path.Combine(Environment.CurrentDirectory, "config/Rooms.cfg");
            string currentLine;
            StreamReader read = new StreamReader(path);

            while ((currentLine = read.ReadLine()) != null)
            {
                String[] parts = currentLine.Split(';');

                string name = parts[0];
                string video = parts[1];
                string isLogged = parts[2];
                string notify = parts[3];
              
                rooms.Add(new Room(name, video, isLogged, notify));
            }

The problem I am running into, is later on, I want to be able to manipulate this rooms array from another form, duely named "AddRoom", so I have done something like this:

 //In AddRoom.cs 
        MainForm.rooms.Add(new Room(textBoxRoomName.Text));
        MainForm.SaveAllRooms();

 //In MainForm.cs
         public static void SaveAllRooms()
        {
            TextWriter tw = new StreamWriter(Environment.CurrentDirectory + "/config/Rooms.cfg");
           
            foreach(Room room in rooms)
            {
                tw.WriteLine(room.name + ";" + room.videoFeed + ";" + room.isLogged + ";" + room.notify);
            }

            tw.Close();
            populateListOfRooms(); //THIS IS WHERE MY LOGICAL ISSUE IS
        }

The problem is, in populateListOfRooms() I want to save the name of each Room in the arraylist rooms to an item in a Combobox.
Because of the fact that SaveAllRooms() and Arraylist rooms are both static, I can not access the specific instance of MainForm
in order to add items to the Combobox.

So I guess essentially my question is, since I can not use a static Arraylist object to store the room data, how can I go about storing these objects in a manner that is accessible from other forms, yet still allows me to access objects in the MainForm (like comboboxes).

I know this post was probably confusing, and definitely longer than it probably need have been, but it's late and so I apologize for any confusion.