The long string of letters can be broken into thirty-two substrings, each of which arose from a two-word phrase in which both words start with the same trigram (or in other words, “tri, tri again,” as the title implies). In each case, that trigram appears in the list of trigrams below the string. For each phrase, that repeated trigram has been deleted, as has one additional letter.

The extra letters, in string order, spell ACTOR RHAMES TWO K POUNDS WNW OPPOSITE, which is a series of three clues that resolve to VING / TON / ESE. One trigram in the list, CHE, has not yet been used; when CHE is inserted into the clued string twice, it produces the answer to this puzzle, CHEVINGTON CHEESE.