on Just Publishing Advice:
Learning how to change passive sentences to active is a skill all writers need. In most instances, all you need to do is move the subject before the verb.
In a passive sentence, there is often the operator word, by before the object. But without one, it can be unclear who or what performs the action.
For example, the book was written in 1972. You could write, the book was written in 1972 by Tom Smith, which is clearer.
But in the active voice, it reads much better and is more concise. Tom Smith wrote the book in 1972.