There is no easy approach how to delete data in Fuseki, because by deleting dataset in Fuseki's web UI you do not delete its data.
One approach could be deleting whole folder including data files in Fuseki's server folder (run/databases/. Problem here is that it can lead inconsistence in the Fuseki's working database.
Second approach would be deleting data by using DROP GRAPH command.
One of the last approaches could be creating non-persistent database. This means that each time you start a new Fuseki instance, you need to create a graph and upload its data.