Query basics - subselecting from entries

I feel like I must be missing something here…

There are times when I do not want to loop over entries, but rather select one based on id (or any other field).

For example, I have a content type called ‘tabHeader’ which has fields of ‘title’ and ‘subtitle’.
I created a tabHeader with title=“I am a title” and subtitle=“I am a subtitle”. It has ID=123.

  1. As far as I can tell, I can’t query contentful just for that one tabHeader, something like:
    client.entries(content_type: "tabHeader", id: 123)
    Is that correct?
  2. Once I have all the entries, with:
    tab_headers = client.entries(content_type: "tabHeader")
    what is the preferred way to subselect from that data?
    I’d like to do something like:
    tab_headers.where(id: 123) or tab_headers.where('title': 'I am a title')
    There’s obviously no ‘where’ method, so how would you suggest I approach this kind of subselect?