public ObservableCollection<Figure> Data { get; set; } = new ObservableCollection<Figure>()
{
    new Figure(20)
    {
        Describtion = "Fruit",
        Color = Xamarin.Forms.Color.FromRgb(240, 125, 100)
    },
    new Figure(5)
    {
        Describtion = "Fish",
        Color = Xamarin.Forms.Color.FromRgb(100, 188, 194)
    },
    new Figure(12)
    {
        Describtion = "Sweets",
        Color = Xamarin.Forms.Color.FromRgb(242, 194, 84)
    },
    new Figure(20)
    {
        Describtion = "Vegetable",
        Color = Xamarin.Forms.Color.FromRgb(142, 215, 131)
    }
};

//change the value of an existing Figure
Data[0].Value = 30;

//add a new Figure to the chart
Data.Add(
    new Figure(20)
    {
        Describtion = "Spices",
        Color = Color.FromRgb(183, 93, 174)
    }
);

//remove a figure from the chart
Data.RemoveAt(1);