Remind yourself of confidence
You need to speak persuasively. At least try to. A low-pitched voice inspires confidence from those around you. Now, here you don’t have to fake it. Just relax before speaking. Keep your lips together and repeat what you want to say in your mind a few times.
Stress can constrict your vocal cords, and can sometimes make your voice come out higher than usual. Sometimes some things are bound to make your heart sink almost instantly.
But the key is to overcome those instantaneous reactions. And only practice and acceptance can help you overcome that.
If you believe that you can, then you will!