Hi! I have had to reset os x server too. You can't realy reset it but if you change your ip address and do a couple things then you will get pretty close to a full reset. If you realy need it all reset wipe your hard drive, then re-install OS X and OS X Server. If you don't want to do that here is another way.
1. Delete the OS X Server app.
2. Go To Library/Sever, then rename that folder to Server old or something like that just not Server.
3. Go To System Prefrences>Network, then where it says configure IPv4 change it to Using DHCP with a manual address.
(If you made a DCHP Resveration For Your Server Delete It Now)
4. Where it says IP Address put in any number like this 10.0.1.(2-200)
5. Click Apply
6. Restart Your Computer
7. Download A New Copy Of OS X Server From The App Store.