There is a car park at the road end at Waipatiki Beach from where you should walk for a few minutes to the left (north) to where large boulders lie on the shoreline.
Very large rockfalls have occurred from the cliffs at the south end of the beach between 2015 and 2017 and it is no longer recommended to explore there due to the hazard. The track has been partly destroyed by these cliff falls.
Instead turn left as you reach the beach and visit the rocks at the north end which include exactly the same strata and types of fossils. Note there is still a hazard, so use your own judgement, and avoid visiting in very wet weather.
There are boulders on the beach that can be investigated, or you can climb up to a narrow path and follow it below the base of the cliffs for a short distance to access the shoreline a bit further away from the beach. It is likely to require some scrambling over some large, slippery and sharp boulders.