OK, I have figured it out, located and changed the config.php and everything now works fine.
I now understand why there is not much detailed help out there on Synology NAS's as you can REALLY ruin everything on your NAS, and becasue of that no one wants to be part of this.
Here's what I did, but I can't accept any responsibility if you damaged anything, or something doesn't work.
Synology NAS's run a Linux type of OS, so you'll need to know about command like dir, ls pwd and vi (the editor)
I managed to get inside the NAS by using Putty set to ssh.
Then I navigated to the installation folder of moodle (I did a bunch of screenshots as I installed moodle)
I learned the vi text editor by changing some text in the README.txt file in this folder, saving it and reviewing the results.
When I was satisfied that I understood what I was doing I changed the ip address in the config.php file and saved it, and exited the putty session.
I then entered the ip address in my the browser xxx.xxx.xxx.xxx/moodle
and bingo I was in.
Thanks for your assistance.
Rich