Make ActionResult Asynchronous in ASP.Net MVC Core

I would make asyn an insert of order and relative orderItems that take

some times...

 The code is raw sql command of EF core

        public IActionResult Create([FromBody] CreateOrderModel model)
        {
            var lastId = _ctx.Riorcl.Select(x => x.Id).DefaultIfEmpty().Max();
            int rowsRiorcAdded;
            using (_ctx)
            {
                AddOrdcli(model);
                rowsRiorcAdded = AddRiorcl(model, lastId);
            }
            return Ok(rowsRiorcAdded);
        }

        private int AddRiorcl(CreateOrderModel model, int lastId)
        {
            int rows = 0;
            foreach (var item in model.OrderItems)
            {
                var addRiorcl = "INSERT INTO OrderItems (Id, ...) " +
                         " VALUES ( @Id... )";

                var Id = new SqliteParameter("@Id", lastId++);
                ...

                _ctx.Database.ExecuteSqlCommand(addRiorcl, Id,...);

                rows++;
            }
            return rows;
        }

        private void AddOrdcli(CreateOrderModel model)
        {
            var addOrdcli = " INSERT INTO Order ( Id,...) " +
                            " VALUES (@Id, ... ) ";

            v...
            _ctx.Database.ExecuteSqlCommand(addOrdcli,...);
        }