If you want to make some simple next and previous slide buttons, you can find the commands at https://renewedvision.com/propresenter/api/.
I've made it easier for you though.
Here's my SIMPLE HTML for those two things (there are directions in the comments field on what, if anything you need to change).
<!--In the links below, change the IP address, if you want to access pro7 on a different computer, to the IP address of that computer. Also change the port number (after the colon) to the port number shown in the network tab of ProPresenter preferences. If it's the same computer AND the port is already 1025, keep it as is and just open this file in a web browser. -->
<a href="http://127.0.0.1:1025/v1/trigger/next">Next slide</>
<a href="http://127.0.0.1:1025/v1/trigger/previous">Previous slide</>
Paste that into a text document (like in TextEdit for Mac or Notepad for Windows) and save it with the .html extension and it should work.