It is unclear from your question whether you had something done to your lips? If yes, wait long enough until effect of "filler" disappear. If not, symmetry can be improved either by enlargement of smaller side with filler or reducing larger side with surgery.
You should consult an experienced plastic surgeon in your area for detailed evaluation and discuss your options. Good luck.
What can I do about asymmetric lips?
Most of us have asymmetries if photographed.
If you have normal asymmetry this may be improved temporarily with filler, rarely, with lip surgery to thin affected side.