I'm pretty sure Rising Stars/Up and Coming is algorithmic, and it's time-dependent; my comic never wound up on that one, because my initial growth suffered a bit due to formatting mistakes in those critical early months. Once your comic is more than a few months old, it's 'disqualified' from that list, it seems.
That said, I did get front-page promo after I switched to scrolling format, and my comic became a little more successful. That was in Specials/Webtoon Canvas, which is selected by staff. (I had 400 subs at the time.)
As for how to get another promo quickly; there's no way to tell. The majority are staff selected, though I think there must be certain algorithms which push them to the staff's attention. I used a lot of social media hashtags like #CANVASHiddenGems, which I'm pretty sure is how I came to their attention. (That's only for comics under 1k, though.)
Your best bet is to just continue making an awesome comic, and hope the staff take notice! Also, if the growth from this promo helps push you into the CANVAS Top 30 lists, that may help with visibility. (Though I have no idea how those lists work, my comic has been drifting up and down the sci-fi one seemingly at random. It's weird.)
