Actually, the support page doesn't address how to find this kind of file. I did, however, stumble on how to do this. Hopefully this is information that will be useful to other Mac users:
1. In the finder, right click on the openLCA application
2. In the contextual menu, select "Show package contents"
3. This exposes a directory containing folders called "Content" and "jre"
4. Right-click on the "Content" folder and again select "Show package contents" from the menu
5. This exposes three folders. Expand or double click on the folder called "MacOS".
6. There (finally), you will see the openlca.ini file that can be edited as you describe.