Hope the trap works for you as it has for others.
An alternative method that can also work, especially if you have a couple of empty 55 gallon barrels or a large empty tank or other container(s) that can hold your tank water. Drain the tank and pick the fish off the bottom. It is kind of drastic, but it can work very quickly if you have a place to store the DT water. Once the dottyback is removed, use a submersible pump (or bucket) and return the tank water back into the tank without the dottyback. If you work fast, the water swap can be done inside of 20 minutes. (Every time I start to think that I want another flame angel again I recall watching all of the fish flopping around in an inch of water while I netted the flame and I'm over that urge.)
Sometimes fish are trap shy, hope yours isn't.