If you mean this ledge you can try jump then upward dash to get up, then you can go left to continue. I probably will add ingame guide for this in the update.
Viewing post in Dawn of Mallumo jam comments
During my first playthrough, it seemed to be working. I tried many times in many different ways and just couldn't reach the platform, however I gave it a second try tonight after rebooting my computer and it seems to be working fine—so it may have been something on my end, especially if no one else had this happen.