Reference: Steps to modify a Sitecore Pipeline

Here are some simple steps for you to remember what to do when you are trying to modify your pipeline in Sitecore.

1. Determine the pipeline you want to modify: Before you start modifying a pipeline, you need to determine which pipeline you want to modify and what you want to achieve with the modification.
2. Create a new class: Create a new class in your Sitecore solution and inherit from the Sitecore.Pipelines.PipelineProcessor class. This class will define the processing step for the pipeline.
3. Override the Process method: Override the Process method of the PipelineProcessor class and add the logic you want to implement in your processing step.

using Sitecore.Pipelines.RenderField;

public class AddHeaderProcessor : RenderFieldProcessor
{
    public override void Process(RenderFieldArgs args)
    {
        args.Result.FirstPart = "<h1>Header</h1>" + args.Result.FirstPart;
    }
}

4. Create a config file: Create a new config file in the App_Config/Include folder of your Sitecore solution, with a name that corresponds to your new class.

5. Add a new processor node: In the config file, add a new processor node within the appropriate pipeline node. The processor node should reference your new class and define the order in which your processing step should be executed in the pipeline.

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <renderField>
        <processor type="Example.AddHeaderProcessor, ExampleAssembly" />
      </renderField>
    </pipelines>
  </sitecore>
</configuration>

6. Deploy and test: Deploy your solution to your Sitecore environment and test your modification to ensure that it works as expected.

Please note that the exact steps may vary depending on the pipeline you are modifying and the specific requirements of your modification.