Writing a value to the Firebase requires that you know the complete, exact path where you want to write. It doesn't support so-called update queries, where you send a query and a write operation to the database in one go. Instead you will have to:

1. Execute the query.
2. Loop over the results.
3. Update each of them in turn.

So in your case that'd be something like:

let query = dataBase.ref().orderByChild('en_word').equalTo('pretend');
query.once("value").then((results) => {
  results.forEach((snapshot) => {
    snapshot.ref.update({
      en_word: 'Pretend'
    })
  })
})