I am trying to find out the entity from text input. If there any option to train Alchemy. So that I can modify entity according to my needs.
You can't train the entity extraction from AlchemyLanguage but there are other Watson APIs that you can use to extract entities or concepts from text.
Relationship Extraction: Performs linguistic analysis of the input text. It then finds spans of text and clusters them together to form entities, before finally extracting the relationships between them.
Concept Insights: Helps you annotate concepts and identify conceptual associations from text.
You can quickly test this API Swagger: https://watson-api-explorer.mybluemix.net/apis/concept-insights-v2