The easiest way to use the CrUX dashboard is to launch the read-only one from here:
https://developer.chrome.com/docs/crux/dashboard/#accessing-the-crux-dashboard. You can then bookmark the dashboard it loads for easy repeat access.
You only need to create your own copy if you want to customize it (but then note you'll need to keep it up to date), so personally I prefer the above method.
While the CrUX dataset has over 16 million domains in it, not every site is represented. So it may be that your site is not included. A quick check is to lookup your site in
PageSpeed Insights and see if it returns anything in the "Discover what your real users are experiencing" section.