He doesn't.
Check XO 12958 (link in my post #8).
About halfway through the XO, you will note the access provisions for historians and former presidential appointees, which of course Berger is.
He was in the Archives under a clearance waiver (again, the XO explains it).
I'm certain this is why Bruce Lindsey was involved, as the middleman between Berger and the Archives security staff and the guy who assisted in preparing the formal docs for the waiver.
BTW, Bill Clinton has ultimate adminstrative authority over the classified docs from his administration, and has clearly delegated the legal paperwork to Lindsey, at least in this case.
Including their removal, loss and destruction? Bill Clinton has the authority to order that?