I'm not aware of any way to delete an individual event in either the Google Nest app or the Google Home app.
However, if you have one of the newer Google Nest cameras or doorbells and do NOT have a Nest Aware subscription, then the camera only saves events for the most recent 3 hours:
Just checking in to make sure that you've seen our responses. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.
I appreciate the help, JT.