My younger sister throws tantrums every time she doesn't get what she wants, how do we go about this?

I'll link you a helpful article, but the most important things you should keep in mind is that you should remain calm and level headed. The following article will teach you the step by steps to learning how to address a temper tantrum effectively: https://ph.theasianparent.com/temper-tantrums-a-complete-overview/