Not easy.
How has the plant been left in the intervening period?
This is not usual practice so there will be little telling you what to do, but on the basis that most of your warranties are probably now out of date ( most I know are 12 months in use or 18 months from installation), my advice would be to go back to the end of mechanical completion of the piping etc and start all the pre-comm checks again for everything including the valves.
At telast that way you know where you are starting from in terms of establishing your service and testing intervals and ensuring that the delay has not caused any of the items to seize or become corroded. 24 months sitting there not doing anything might seem like a waste of time, but equally the items were designed to be in operation, no in stores.
Put it this way. Would you be happy to buy a PSV you knew was last tested >24 months ago and since then has been sitting in the open, maybe well sealed, maybe not and then install it without a test?? I wouldn't.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
