There is no extra plugin installer, the plugins are part of the normal full installer that you download.

I assume that your Unreal is too new. Here the line from the system requirement in the FAQs from the e-on download page:

• Unreal Engine 4.26-4.27 & 5.0.-5.1 (5.2 & 5.3 are supported by PlantFactory 2024)

One day your ship comes in - but you're at the airport.