How do I attach key levels to a trade in the journal?

From the trade's own detail panel, where the level fields read from this master list.

Because the dropdowns are fed by the library, the work you do here is what makes tagging fast later. A tidy, well-ordered list of the levels you actually use turns tagging into two clicks; a list of forty levels you picked once and never trade turns it into a search.

If a level is missing when you are tagging, add it here and it is available immediately.