How To Install Magma
To get plugins to work on 1.12.2 Forge we'll need to use something called Magma.
You can download this via our version installer, just select Magma from the drop down.
Head to this link: https://magmafoundation.org/ (opens in a new tab)
Here download the latest version for 1.12.2 and upload it to your server via the file manager
Set the Magma jar in the overview page, and you're all set.
You can now add plugins to the plugins folder in the file manager.