Try this way

string Members = dt.Rows[0]["AssignedMembers"].ToString();
string[] splitMembers = Members.Split(',');
for (int i =1; i <= splitMembers.Lenght ; i++)
{

    string strItem = splitMembers[i].ToString();
    if (int.Parse(strItem) == i)
    {
            CheckBoxList1.Items.FindByText(strItem).Selected = true;
    }

}