Hi there!
Refer to this other thread where I answered how to delete all nodes and relationships in a graph.
--> Efficiently delete all the nodes and edges of a very large graph
Either approach I proposed in this thread will work for you.
If you have access to all of APOC procedures, CALL apoc.periodic.truncate() will also remove all entities (and optionally indexes and constraints) from the database. - reference apoc.periodic.truncate - APOC Documentation (neo4j.com)
Cheers,
Rob