I’m not sure how you could get this implication across in the film. Maybe in the crawl, instead of saying Kylo is searching for the source of Snoke’s power, he’s looking for the Emperor’s lost fleet. Maybe that’s what the Knights of Ren were doing during the last two films, looking for clues to the lost fleet of the Empire.

Dom had a good idea regarding ROTJ, to make Palpatine’s Star Destroyer have those same red stripes. We could even create a shot of the end of the film of it, and other Destroyers, leaving the battle. The blank screen in his throne room could be used of foreshadowing as well.

But yeah, just trying to make that change in Episode IX alone, I would say mentioning it in the crawl would be the the most straightforward way to do that. It almost might not be a bad idea to downplay its scale a little.