Gaps in teeth causing 'whistling' sounds when doing F and S sounds. How do vocal coaches work through it?

Someone told me that everyone have their own unique sounds, but it just sucks that I have two gaps in my teeth (middle upper and lower) that causes me to sound like a kettle. Im aware there are artists with similar case, like Cynthia Erivo. But how do they sound perfectly fine (I know she is wayyyy to good to be an example for me, but still)?

Is it just technique I have to work on? Mouth and tongue placement?. Or am I doomed to be a kettle?. Its really making me feel insecure when singing, especially when the microphone reallyyyy picks up the sharp whistling note I make.