I have just purchased two young hens to add to my free range flock of 5. Unfortunately, they were debeaked. How do I reverse that? Trim the lower beak until it is shorter than the top? What is the best way to do that?
A chicken's beak will grow back over time. Presumably, the beak was trimmed by someone who knew what they were doing. Any attempts on your part to correct by trimming the lower part are likely to just cause more issues.
As a now free range chicken, they should both manage their own beak growth; they may choose to rub the bottom beak against a rock and shorten it, or they may not.
The answer to your question is "just give it time, nature will take care of it".