How do you decrease pepper taste in soup when it is too strong?

Answer

Put a large peeled raw potato into the pot for 1/2 an hour, taste and if still too hot with the pepper, then put another potato in and leave another 1/2 hour.

As an aside....

Peeled, thickly sliced, raw potato has more exposed surface area than a whole one. One can dilute the soup with stock (if possible) or add water and a thickening agent. It may be possible to hide the taste a bit with something else strong, like herbs or a bit of brown sugar.