You install Forge or NeoForge yourself from the GamePanel, in the Minecraft Version menu, without opening a ticket. For a ready-made modpack, use the Modpack Manager instead (Tools menu).
Note the exact version your mods require (e.g. Minecraft 1.20.1, Forge 47.3.0).
Download your files, or create a backup if you have the paid Backups option (Management, Backups): worth doing as a precaution, even though the install keeps your files as long as "Delete all server files first" stays off.
Minecraft Version menu: Forge or NeoForge edition, the version, then Install.
The GamePanel's Version tab: edition on the left, version on the right, Install button Start the server once, then add your mods in one click with the Plugin Manager or upload their files into the
modsfolder, and restart.