ConcurrentActions.cs

var threads = new Thread[2];
threads[0] = new Thread(async () =>
{
    using (var dbContext = new MyDbContext())
    {
        var account = await dbContext.BankAccounts.FindAsync(1);
        account.Credit(100);
        await dbContext.SaveChangesAsync();
    }
});
threads[1] = new Thread(async () =>
{
    using (var dbContext = new MyDbContext())
    {
        var account = await dbContext.BankAccounts.FindAsync(1);
        account.Debit(200);
        await dbContext.SaveChangesAsync();
    }
});
foreach (var t in threads) 
{
    t.Start();
}