The same way non-billionaires do: there isn’t anything that money can do about it. While ‘only’ worth $150m, Katherine Brosnahan (you may know as Kate Spade) tragically hanged herself last week after suffering for a few years. If $150m can’t buy you out of it, I’m not sure another $850m would. https://en.wikipedia.org/wiki/Kate_Spade#Death
You can use some of that money to buy Alprazolam / Clonazepam :-). They're available as relatively inexpensive generics at this point. Maybe not an option if you are totally broke / impoverished, but certainly something billionaires have access to.
Throwing around alprazolam/clonazepam as a solution for anxiety is trite and can be damaging. Take caution with them.