Dead Live Rock...?

[DSlater]

Hey guys - we're fairly new to the reefing hobby. We have a 20 gallon nano system that's 3 mths old. We decided to go bigger and are purchasing a 240 gallon tank but all the live rock was taken out and placed outside to dry/die. What are our best options in bring this rock back to life? I've been told to powerwash it then recure it in the dark for a couple of mths with a skimmer and to use Microbacter 7. After that place a few pieced of live rock in there and let it reseed. Any thoughts?
Cheers!