How to get my chin to point downwards instead of upwards? (Photo)

Typically chins point upward because the bone is vertically short. But that is not the case in you in which it is the excessive soft tissue chin pad that points upward with what appears to be adequate vertical chin length. It its interesting and helpful that you have had filler placed and got some improvement. Where the filler was placed and what type of chin shape change that resulted is critical information to device a surgical procedure that can do the same (and more so) with a permanent effect. Unfortunately it is hard to appreciate the effects of the filler which I can only assume was placed more on the bottom of the soft tissue pad to fill it out more and help make it look less pointed upwards?? If so then an opening intraoral bony genioplasty to tilt the chin bone and soft tissue chin pad more downward could be what you need.,

Your growth pattern is called 'low angle' whereby the top and bottom jaws grow more horizontally (often the upper teeth don't show a lot as well). The jaw 'body' often has the 'curve' you note. There are a couple of methods to change it - one involves a more significant 'rotation' of the jaws which needs to be explained by the surgeon in person. Altering just the chin can help as long as you are realistic in this second approach.