How did charlie save wilkie-book-private peaceful?

It seems you might be mixing up characters and stories. Charlie is a character in the book "Charlie and the Chocolate Factory" by Roald Dahl, while "Private Peaceful" is a novel by Michael Morpurgo, telling the story of Tommo Peaceful during World War I.

There is no character named Wilkie in either book, and Charlie does not play a role in "Private Peaceful."

Perhaps you are thinking of another book or story?