I don't believe there is a way to set your dashboards back to factory defaults (although I could be wrong, in which case someone please correct me). The way I do it is if I want to modify a default dashboard, I create a copy of it and modify the copy. The other way would be to export a copy to a specific location before you edit it in case you ever need to revert back.
But all of that information above falls in the too late category. So if I were you I would spin up a new vROPs node/cluster really quickly as a new instance (ie separate from your current environment), and export the default dashboards, then import them into your current environment. Does that make sense?
Let me know if you need me to be more specific.