To make a borderline page cross the index threshold, raise both its value and its discoverability: add unique value and information gain that distinguishes it from duplicates, strengthen internal links to it from pages that already get crawled, improve its quality and intent-fit, remove or consolidate the near-duplicate pages competing with it, and then request indexing. The move is add value plus improve discoverability together. A borderline page is one the system has judged barely worth keeping, so the job is to push it clearly over that line on both fronts at once.
The value half is what actually changes the verdict. Give the page something a searcher could not get from existing pages, a genuine angle, data, depth, or perspective that adds information gain, so it stops reading as a near-duplicate and starts being worth storing. Tighten its quality and make sure it squarely answers the intent it targets. If sibling pages of your own are splitting the same value, consolidate them so one strong page replaces several weak near-duplicates rather than competing with itself.
The discoverability half makes sure the improved page is found and re-evaluated. Link to it from pages that are already indexed and crawled regularly, so the system has a clear path to it and a signal that you consider it important. Make sure it is reachable and not buried. Then request indexing directly so the page gets looked at again rather than waiting on the next crawl. Note that “just resubmit it” without raising value does nothing, and “add more words” is not the same as adding value; padding length without adding information gain leaves the page borderline.
For your next stuck page, work both levers in order. First give it real unique value and fix its intent-fit and any near-duplicate competition, then strengthen the internal links pointing to it and request indexing. Raise the page’s value and its discoverability together, and you give a borderline page the clear reason and the clear path it needs to cross the threshold.