Once you associate the asset event to a specific asset, it won't let you delete it due to a complex design of asset tables in database. Still if you'd like to remove the event permanently from the asset, you might delete the asset completely and recreate the asset which can be inconvenient.
Therefore if possible, we recommend that you create asset events first in the "Lookup Tables" and carefully log the event to an asset later. You can create/delete/locate all asset events listed in Settings, CMMS Settings, Lookup Tables and Asset Events, but the events should have no association with any asset for removal.