//Use SetHistoricPrices to add quote history to an instrument
var client = new BFSServiceReference.bfsapiSoapClient();

var credentials = new BFSServiceReference.Credentials()
{
    UserName = bfsusername, //Username of administrative user in your instance of BFS
    Password = bfspassword, //Password of the administrative user in your instance of BFS
};

var response = client.SetHistoricPrices(new BFSServiceReference.SetHistoricPricesRequest()
{
    Credentials = credentials,

    identify = bfsidentifier, //Identifier is a unique token for your instance of BFS    

    PriceDateEntries = new PriceDateEntry[]
    {
        new PriceDateEntry()
        {
            AssetId = new Guid("7f1478ff-62a8-42a5-bff5-8487f72d7861"),
            Price = 100,
            PriceDate = DateTime.UtcNow,
        },
        new PriceDateEntry()
        {
            AssetId = new Guid("7f1478ff-62a8-42a5-bff5-8487f72d7861"),
            Price = 100,
            PriceDate = DateTime.UtcNow.AddDays(-1),
        },
        new PriceDateEntry()
        {
            AssetId = new Guid("7f1478ff-62a8-42a5-bff5-8487f72d7861"),
            Price = 100,
            PriceDate = DateTime.UtcNow.AddDays(-2),
        }
    }

});

Console.WriteLine(response.Message);