A little asymmetry is completely normal, since no one has perfectly matched brows. If it bothers you, there are a few good options. Eyebrow transplantation can add hair to the thinner or shorter brow, or reshape the beginning, arch or tail so that both sides match more closely. It is done with small, single hair grafts placed at the natural angle, and the result is permanent. If you prefer something non surgical, you can use brow pencil or powder, brow tinting, or microblading or micropigmentation to even out the shape, which has less downtime but needs touch ups. Minoxidil or other topicals can sometimes help a sparse brow but results vary. The right option depends on whether the difference is in hair density, shape, or the position of the brow bone and skin. A consultation with photos from the front would help me tell you which is best for you.