As someone said, usually you don't call it directly for security reasons. But If yo are just looking to test then you can do it just like you do it locally:

Write a service for retrieving an object:

public static class UserService
{
    private const string server = "";
    private const string database = "";
    private const string username = "";
    private const string password = "";

    private static string connectionString => $"Data Source={server};Database={database};User Id={username};Password={password}";

    public static async Task<UserDto> GetUserAsync(string username, string password, CancellationToken cancellationToken)
    {
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            string sql = "SELECT * FROM MyTable WHERE Column = @value";
            return await connection.QueryFirstOrDefaultAsync<UserDto>(sql).ToList();
        }
    }
}

Then in your button call just call the service:

var user = UserService.GetUserAsync("John Doe", "abcd1234");