c# anonymous type add new items : I must add new items to anonymous type. I have tried a lot of solutions but it doesn't work.

Code:

            for (int i = 0; i <= diff.Days; i++)
            {
                if (!(literByBeerBrand
                    .Any(y => y.date == firstDate.ToString("yyyy-MM-dd"))))
                {
                    var t = new
                    {
                        value = 0,
                        date = firstDate.ToString("yyyy-MM-dd")

                    };
                    // HERE I MUST ADD NEW ITEM TO ANONYMOUS TYPE
                }

                firstDate = firstDate.AddDays(1);
            }
I have tried before

    1) literByBeerBrand.ToList()[literByBeerBrand.ToList().Count()] = t;
    
    2) literByBeerBrand.ToList().Add(new
                    {
                        value = 0,
                        date = firstDate.ToString("yyyy-MM-dd")
                        
                    });

 