This is generations old method.
Apply oil all over the scalp. Traditionally it is cocoanut oil, but baby oil would do. This is better than applying Vaseline jelly when it comes to washing off. The oil has tendency to run. So just apply a drop or two and spread on the scalp with fingers, Repeat the process till the scalp is completely covered. If oil bothers you, use shower cap to cover the hair and hold back the drip. Needless to say, please cut hair as short as you can stand which will make the oil application easy.
Keep oil at least for a few hours. Use lice comb if you have one. Shampoo off the oil. Repeat this for consecutive 3-4 days.
Then repeat the process 3-4 days apart. Even you have removed the lice, the eggs may not be combed away. These eggs become lice in a few days, so you need the application every few days. You can increase the time interval between two applications slowly and then stop.
The idea is to drench the lice in oil, which kills them. But the eggs survive. So, when the eggs germinate, repeat the process for new batch of lice.
The oils are without chemicals. But the process is tedious and needs lots of patience.