If you mean the one on most popular it has a google drive link, there are many versions of Octalien you can pick from
https://itch.io/jam/day-6/topic/3031465/itchio-presentation-guide
I use ShareX (desktop tool to record mp4 low res clips) and ezgif website to convert into .gifs lower than 3mb
I use photoshop in addition to this but only for thumbnail and header, photpea is a free online tool in replacement of photoshop
Full Guide is here: https://itch.io/jam/day-6/topic/3031465/itchio-presentation-guide