Access difficulties

I’m a new admin on an existing site, and we just switched domains from .com to .org.
I can “visit site” and see the existing website intact, but the dashboard shows only the introductory “hello world” post and “sample” page.
Any thoughts on how to access the old site to edit it? I do Not wat to rebuild it from scratch if i don’t have to…
I checked with the website hosts and they don’t know what to tell me – any thoughts are welcome at this point.