How can make my hair thick and healthy.?

thick hair is mostly genetic

hair mask and oil! also cut ur edges often, and for thicker hair maybe get extensions since there's not much that can be done about that (unless it's thin due to unhealthiness)

Girl, you wouldn’t believe it—my hair used to be extremely thin. I was born with it, and you could see my scalp at a glance. Every salon I went to told me my hair was too thin and refused to do any heat styling (though I still did it anyway ).

Now my hair has become so much thicker because I started applying a deep oil treatment 40–50 minutes before washing. The key is to understand your hair type and choose the right oil for it.