Telegex.set_chat_photo

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

set_chat_photo(chat_id, photo)

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Specs

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

Use this method to set a new profile photo for the chat. Photos can't be changed for private chats. The bot must be an administratorin the chat for this to work and must have the appropriate admin rights. Returns True on success.