[Assistants API] how to create a thread from an existing assistant?

In the current API specification OpenAI Platform,

we do not see a way to create a thread using an existing assistant.

you do not need to create a thread from an existing assistant, or any assistant. a thread can be created on its own, and its used to facilitate a series of messages between a particular assistant and the user. a new thread means a new conversation with no message history, and you can use as many as you want with an assistant. either use the same one or create a new one.

POST - https://api.openai.com/v1/threads
POST - https://api.openai.com/v1/threads/{thread_id}/messages

OR

POST - https://api.openai.com/v1/threads/runs