What would be the best way to fill in the dip above my chin implant? (Photo)

If you are that much concerned with this "dip" I would suggest a trial with soft tissue filler. If you like result, a more permanent solution can be achieved either with permanent filler or small addition to chin implant. Good luck.

 Hi, I have performed many Chin Augmentations using chin implants and dermal fillers for over 30 years.  From the photos, your mental crease is quite deep and your request to fill it, so its appearance is softened, seem very reasonable.  A dermal filler will fill and soften the mental crease.  
Hope this helps.

This is a common issue with implants and even genioplasty whereby the surgeon should consider the entire contour from the lip position/contour to the chin; including the height. If you have an implant in place; you could 'add' a small strip/hand carved to the bone underlying the fold - quite simple. You also appear to have a slight 'dip'/shadow alongside the implant and that could be managed as well. The second choice is to use filler; but scarring sometimes prevents obtaining the best 'S' curve to the area; but it is fair to try it out.