Custom map at the contact page
We don't use default Opencart contact page data in our theme, we prefer to use custom Journal modules for greater flexibility.
So all the default contact page details have been hidden from Journal > Skins > Edit > Contact... and instead we use custom Journal modules such as Blocks, Info Blocks, and Contact Form added to the contact layout in Journal > Layouts > Contact.
For the map, you need to create your own map in Google Maps and copy the embed code and paste it into your Journal Blocks module. The demo map is just a demo with a random address.
Here's info on how to generate your own map code https://support.google.com/maps/answer/3544418?hl=en
Once you have the iframe code you can paste that in the Block Content in your Blocks module in Journal > Modules > Blocks > Your Module (the one with the map) > Block > Block Content. (You can also input a map height in the provided field below the map code).