Hey there,
a tic like that could be caused by any number of things, and if the doctor is not worried, they clearly do not expect it to be anything serious.
In terms of natural remedies, consider switching to a nutrient dense whole food diet, one specifically rich in stuff that the brain and nerves need to grow and repair and function well.
For more info watch Georgia Ede on YouTube she details a brain healthy diet really well. Basically a child's brain and nervous system are being built out of protein and fat, so we all need to make sure these nutritional needs are being met with high quality complete proteins, from animal sources as they are complete proteins, i.e contain all the essential amino acids necessary, and healthy natural fats, like those found in meat, dairy, cheese, but also avocado, olive and coconut oils. It is possible to get all the essential amino acids form non-animal sources, but you need to carefully balance your sources, as protein sources from beans or pulses etc. are incomplete.
Sounds too simple to help, but our nervous systems need to be built and maintained out of these things, so we need to consume them.
It might also help cutting down on processed foods and processed carbohydrates as these can be inflammatory, again not good for the developing brain and nervous system.
I wish you the best of luck, and you and your child all the best.