using System;
using System.Data;
using Devart.Data.BigQuery;
...
class Program
{
    static void Main(string[] args) {

        const string connectionString = @"Authentication Type=ServiceAccount;ServiceAccount Json=C:\keys\service-account.json;Project Id=your_project;DataSet Id=your_dataset;License Key=**********";
        const string sql = "SELECT deptno, dname, loc FROM dept ORDER BY deptno";

        using (BigQueryConnection connection = new BigQueryConnection(connectionString)) {

            connection.Open();
            DataTable table = new DataTable("Dept");

            using (BigQueryCommand command = connection.CreateCommand()) {

                command.CommandText = sql;
                using (BigQueryDataAdapter adapter = new BigQueryDataAdapter(command)) {

                    adapter.Fill(table);

                    adapter.UpdateCommand = new BigQueryCommand("UPDATE dept SET loc = @loc WHERE deptno = @deptno", connection);

                    adapter.UpdateCommand.Parameters.Add("deptno", DbType.Int64).SourceColumn = "deptno";
                    adapter.UpdateCommand.Parameters["deptno"].SourceVersion = DataRowVersion.Original;
                    adapter.UpdateCommand.Parameters.Add("loc", DbType.String).SourceColumn = "loc";

                    DataRow firstrow = table.Rows[0];
                    firstrow["loc"] = "BOSTON";
                    Console.WriteLine(adapter.Update(table));
                }
            }
            Console.WriteLine("Rows after update.");

            foreach (DataRow row in table.Rows) {
                Console.WriteLine("{0}\t{1}\t{2}", row[0], row[1], row[2]);
            }
        }
        Console.ReadKey();
    }
}

Imports System
Imports System.Data
Imports Devart.Data.BigQuery
...
Module Program

    Sub Main()

        Const connectionString As String = "Authentication Type=ServiceAccount;ServiceAccount Json=C:\keys\service-account.json;Project Id=your_project;DataSet Id=your_dataset;License Key=**********"
        Const sql As String = "SELECT deptno, dname, loc FROM dept ORDER BY deptno"

        Using connection As New BigQueryConnection(connectionString)

            connection.Open()
            Dim table As New DataTable("Dept")

            Using command As BigQueryCommand = connection.CreateCommand()

                command.CommandText = sql
                Using adapter As New BigQueryDataAdapter(command)

                    adapter.Fill(table)

                    adapter.UpdateCommand = New BigQueryCommand("UPDATE dept SET loc = @loc WHERE deptno = @deptno", connection)

                    adapter.UpdateCommand.Parameters.Add("deptno", DbType.Int64).SourceColumn = "deptno"
                    adapter.UpdateCommand.Parameters("deptno").SourceVersion = DataRowVersion.Original
                    adapter.UpdateCommand.Parameters.Add("loc", DbType.String).SourceColumn = "loc"

                    Dim firstrow As DataRow = table.Rows(0)
                    firstrow("loc") = "BOSTON"
                    Console.WriteLine(adapter.Update(table))
                End Using
            End Using
            Console.WriteLine("Rows after update.")

            For Each row As DataRow In table.Rows
                Console.WriteLine("{0}" & vbTab & "{1}" & vbTab & "{2}", row(0), row(1), row(2))
            Next
        End Using
        Console.ReadKey()
    End Sub

End Module

using System;
using Devart.Data.BigQuery;
...
class Program
{
    static void Main(string[] args) {

        const string connectionString = @"Authentication Type=ServiceAccount;ServiceAccount Json=C:\keys\service-account.json;Project Id=your_project;DataSet Id=your_dataset;License Key=**********";
        const string sql = "UPDATE dept SET loc = 'SEATTLE' WHERE dname = 'SALES'";

        using (BigQueryConnection connection = new BigQueryConnection(connectionString)) {

            connection.Open();
            using (BigQueryCommand command = connection.CreateCommand()) {

                command.CommandText = sql;
                Console.WriteLine(command.ExecuteNonQuery());
            }
        }
        Console.ReadKey();
    }
}

Imports System
Imports Devart.Data.BigQuery
...
Module Program

    Sub Main()

        Const connectionString As String = "Authentication Type=ServiceAccount;ServiceAccount Json=C:\keys\service-account.json;Project Id=your_project;DataSet Id=your_dataset;License Key=**********"
        Const sql As String = "UPDATE dept SET loc = 'SEATTLE' WHERE dname = 'SALES'"

        Using connection As New BigQueryConnection(connectionString)

            connection.Open()
            Using command As BigQueryCommand = connection.CreateCommand()

                command.CommandText = sql
                Console.WriteLine(command.ExecuteNonQuery())
            End Using
        End Using
        Console.ReadKey()
    End Sub

End Module