You will want to use the MyDrive site at TomTom to work on either routes or Points of Interest for your GO 500. If you haven't already downloaded the MyDrive Connect software for your device, start here >>
https://www.tomtom.com/en_gb/mydrive-connect/
Scroll down a bit and you'll see download options for both Windows and Mac.
You will need to create an account for your GO 500; that will require an email address and a password of your choosing.
Once you have MyDrive connect up and running, you will find a tab called "MyDrive - Plan routes and view traffic". That will take you to the online web page where you will use the same login information that you used to create your GO 500 account.
From there, you can, among other things, load Point of Interest files to your device. I suggest this because there are such files already built for things like 'caravan sites', and those files can be directly installed on your GO 500. One site that offers such a file for caravan and similar sites is here >>
https://www.gps-data-team.com. I am attaching a *.zip file of their UK offering to this message that contains the file. TomTom uses *.ov2 files for their Points of Interest.
From left side of the MyDrive web page, you can select the third icon from the top -- looks like a bubble with a face and arms? - then select POI Files and upload the attached caravan *.ov2 file. With your GO 500 unit connected, that data will transfer to it, and you will find under My Places on your 500 the full list of campsites that was included in the file.
Once you have that bit sorted, let me know and we'll talk about whether you need to prepare a route, or whether having access to the POI is enough to work with.