Check vSphere history tasks in Monitor\Tasks & Events\Tasks.
But, it has time limit.
How do I check earlier tas
You can use PowerCLI. If you're still not seeing it, it has been aged out of the database. This happens automatically.
What command should I use？
Get-Task - PowerCLI System.Collections.Hashtable.ModuleName Help Reference
You can export events to CSV file. in vSphere Client go to File -> Export -> Events
How do export events on the vSphere web client?
Try this: Export Events Data in the vSphere Web Client