Traits

Modifies the typing of your Pokemon, may be applied up to three times.

This can either change or add on to a Pokemon's original typing, you can choose!
However, a Pokemon can only have a maximum of 3 types, meaning triple elementals must replace their original typing (unless one of the Elemental traits is the same as their original typing)

If your Elemental type rolled is the same as the Pokemon's original typing, it may be used to enhance their pre-existing type in some way.