How to clear old requests to make fresh requests for documentation

Hi,
I am trying to make my first documentation of an API. I have deleted all the requests relating to the API from history but when I start creating the documentation, I still find the old requests.

How can I erase those old requests from the memory so as to document with new requests?

You have to delete the request from the collection and not history to update the documentation. You can refer this for further information https://learning.getpostman.com/docs/postman/api_documentation/intro_to_api_documentation.