A vertical chin cleft is primarily a result of a midline soft tissue deficiency/separation. While there may be a notch in the underlying chin bone that is not a primary contributing factor. While the absolute and permanent solution is to do an external excision and closure, the resultant scar for a female would be unacceptable in most cases. (although with your already wider chin this is really the best approach in your case) Thus the alternative approach is to add volume under the vertical chin cleft. Injectable fat grafting would be the simplest approach and is what should be done first to see how much improvement can be obtained. This can also be tested initially with either injectable fillers or even saline injections. The only aesthetic problem with adding volume in your case is that it will make the chin bigger which creates another aesthetic problem. The only vertical chin reduction technique that will not case any other aesthetic issues is an internal approach to bring the mentalis muscle together which helps push out the cleft and will even make the chin a bit more narrow.
You will need a combination of strategic micro-liposuction, fat grafting, and redundant skin excision to improve your chin contour. This can be done in the office with no sedation for a very affordable price.
usually, the cleft/dimpled chin is a combination of the underlying bone shape and the separation of the 'mentalis' muscle in the area. It definitely can be altered by a genioplasty which contours the area and 'unites' the mentalis tissue.
A cleft chin can be fixed. It depends on the cause. Usually, it is the result in a defect in the underlying jaw bone (mandible). A pre-operative x-ray would delineate that and the bone can be filled in. If it is a result of a soft tissue issue (usually the mentalis muscle) then the muscles can be brought together. Best wishes.