It’s in the FCTM.
PR>AEP>MISC. but there’s no pretty picture, unlike in the Safety First article June 2019 on managing over speed events. The procedures were changed a couple of years ago if you’re reading an old safety first. I think it was in the FCOM previously
I recommend getting the Safety first app. It’s a very good portal that allows you to dig out and search articles (not just the mag PDF).
Even better is the Airbus WIN video on managing speed. Again get the app. It has a good overspeed section.
Overspeed mismanagement have have caused a large number of in flight upsets in recent times. Last 2 Airbus safety conferences have had sessions on just this topic. Your tech pilot/training dept/safety dept should be able to dig the presentations out of Airbus world.