Can someone please direct me how to set up Grafana correctly, as a noob.
On Prymont Testnet, when I simply click on premade prysm-prymont Dashboard, I getting this result:
But on the otherhand, my validator is working great, when I look at stats in validator itself.
Sorry if I missed something trivial, and if the question is too noobish, I simply never worked with it before 
At first I had the same issue as you but over time the data was updating and now it’s showing data for me. You still have this problem?
I had it this morning still (12-15 hours after posting).
Now I’ve uninstalled Prymont to do some other tests, so I cannot tell unfortunately.
But same happened with Medalla, for whole month maybe, as I was testing it…
Change the setting in the top right hand corner from 7 Days to a few mins. if it’s configured correctly you will see data quicker
Thank you again @AJR for the advice, I’ll try that. 
Also make sure of having DAppNode Exporter installed.
