To my knowledge this should be automatically set by Node-Red-Dashboard in the graph widget. You might check settings in the graph widget node and possibly ask a question on the node-red community forum(be sure to tag with node-red-dashboard).
I have seen this once. I believe it was caused either a memory issue which required a reboot after a lot of deployments, or you may need to downgrade your dashboard library version.
Can you see if the issue persists after a reboot of the edge computer?
Can you send a screenshot of your Palette Manager. It can be found in the three horizontal line menu in top right > Palette Manager.
How do I update my node-red library when I couldn’t connect to the internet connection whenever I’m connected to the Edge Computer, I have to switch to my own Wi-Fi connection whenever I needed to use the internet.