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.
For example, is the game Pokemon is spelled with an 0 or an A? Try Pokem?n .