在ASP.NET Core Web API中，根据聚合分割控制器需要遵循以下步骤：

1. 定义聚合类：根据业务逻辑定义聚合类，例如Order（订单），Customer（客户）。

2. 创建控制器：为每个聚合创建控制器，例如OrderController，CustomerController。

3. 为每个控制器定义路由：在控制器上使用Route特性定义路由，例如：[Route("api/orders")]，[Route("api/customers")]。

4. 在控制器中实现HTTP方法：根据业务需求实现GET、POST、PUT、DELETE等HTTP方法。

下面是一个简单的ASP.NET Core Web API聚合控制器示例：

using Microsoft.AspNetCore.Mvc;

namespace MyAPI.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class OrderController : ControllerBase
    {
        // Get method to retrieve order by ID
        [HttpGet("{id}")]
        public ActionResult GetOrder(int id)
        {
            // implementation details
        }

        // Post method to create new order
        [HttpPost]
        public ActionResult CreateOrder(Order order)
        {
            // implementation details
        }

        // Put method to update existing order
        [HttpPut("{id}")]
        public ActionResult UpdateOrder(int id, Order order)
        {
            // implementation details
        }

        // Delete method to delete order by ID
        [HttpDelete("{id}")]
        public ActionResult DeleteOrder(int id)
        {
            // implementation details
        }
    }

    [Route("api/[controller]")]
    [ApiController]
    public class CustomerController : ControllerBase
    {
        // Get method to retrieve customer by ID
        [HttpGet("{id}")]
        public ActionResult GetCustomer(int id)
        {
            // implementation details
        }

        // Post method to create new customer
        [HttpPost]
        public ActionResult CreateCustomer(Customer customer)
        {
            // implementation details
        }

        // Put method to update existing customer
        [HttpPut("{id}")]
        public ActionResult UpdateCustomer(int id, Customer customer)
        {
            // implementation details
        }

        // Delete method to delete customer by ID
        [HttpDelete("{id}")]
        public ActionResult DeleteCustomer(int id)
        {
            // implementation details
        }
    }
}