You already know that the asterisk (*) acts as a multi-letter wildcard operator, meaning it will look for multiple substitute letters. You can use it to expand a root “word” such as “testa.” If you search for testa*, your results may include words like testamentary, testator, testable, etc.
If you need just need to substitute one letter, use the question mark (?) as a single-letter wildcard operator.
Not sure whether the game Pokémon is spelled with an “o” or an “a”? Try Pokem?n. You may be surprised at the variations that come up!