Telegex.set_chat_title

You're seeing just the function set_chat_title, go back to Telegex module for more information.
Link to this function

set_chat_title(chat_id, title)

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Specs

set_chat_title(integer() | String.t(), String.t()) ::
  {:ok, boolean()} | {:error, Telegex.Model.errors()}

Use this method to change the title of a chat. Titles can't be changed for private chats. The bot must be an administrator in the chat for this to work and must have the appropriate admin rights. Returns True on success.