Can chin filler migrate to the neck? Will it dissolve on its own?

Different Hyaluronic Acid (HA) fillers have various properties. Depending on which type of filler you had injected, you may be at a higher risk of migration. Also, if filler is injected in areas where there is a lot of sheer or movement (like in certain areas of the face/chin), it is a possibility for filler to migrate.
Most immediately, the chin fill may migrate down to the area under your chin (submental area). This area is noticeable on the side and is the target for neck rejuvenating procedures like facelift/necklift, liposuction, FaceTite, kybella.
If this was an HA filler, it may resolve on its own over the course of months (depending on how much was injected and which type of filler. However, if it is bothersome, you may opt to have an enzyme injected to those areas of suspected migrated filler to dissolve the filler instantaneously. The enzyme itself is called hyaluronidase, which dissolves HA or hyaluronic acid fillers. There are several major brands of hyaluronidase; two common ones are hylenex and vitrase.
Anecdotally, some injectors argue that vitrase is more potent and effective when compared to hylenex. Others say there is no difference. Regardless, it may be worthwhile to undergo a round of enzyme injection to try to dissolve any possible migrated filler in the areas of interest.

For unique cases where a variety of modalities could be used to treat the condition, I would suggest an in-person or virtual consultation to develop a custom and effective treatment plan. It is difficult to precisely define the best option without collecting the same information. I suggest reaching out to an expert for a consultation with surgical and non-surgical methods to get a comprehensive option. Best, Dr. Emer.