Fill or Filter combobox based on vslue from anothe comobobox

[RJL1]

I have 2 combo boxes. I have a counted by combobox which is populated with a list of users that can cycle count product. My second box comes from the same table and is a list of the warehouses where this users is allowed to cycle count.

I need to be able to update the second combobox (list of warehouse) based on the user selected on the first combobox. This would be a list of warehouse the slected user on the first combobox has access to.

Here is my code so far. The first combobox (user) is populated whe nthe form load. I need to populate the second box based on what is sledcted on te first and refresh second combobox if the selection chnages on the first combobox.

        private void cmbCountByFill()
        {
            da.SelectCommand = new SqlCommand("SELECT DISTINCT W.USER_NAME, U.DESCRIPTION FROM WAREHOUSE_ACCESS W LEFT OUTER JOIN USER_PROFILE U ON U.USER_NAME = W.USER_NAME WHERE U.CYCLE_COUNT_PREFERENCE = 'Inventory Control'", cs);
            {
                DataTable dt = new DataTable();
                da.Fill(dt);


                cmbCountBy.ValueMember = "USER_NAME";
                cmbCountBy.DisplayMember = "DESCRIPTION";
                cmbCountBy.DataSource = dt;

                cmbCountBy.DropDownStyle = ComboBoxStyle.DropDownList;
                cmbCountBy.AutoCompleteSource = AutoCompleteSource.ListItems;
            }
        }

        private void cmbWarehouseFill()
        {
            da.SelectCommand = new SqlCommand("SELECT DISTINCT A.WAREHOUSE FROM WAREHOUSE_ACCESS A", cs);            
            {
                DataTable dt = new DataTable();
                da.Fill(dt);
                
                cmbWarehouse.ValueMember = "WAREHOUSE";
                cmbWarehouse.DisplayMember = "WAREHOUSE";
                cmbWarehouse.DataSource = dt;
                
                cmbWarehouse.DropDownStyle = ComboBoxStyle.DropDownList;
                cmbWarehouse.AutoCompleteSource = AutoCompleteSource.ListItems;
            }
        }

I'm new to C# so any help with this is appreciated

Thanks