You really should list more info so we can better assist.
Computer OS (32 or 64)
Plug-in installed (32 or 64 bit)
Generally speaking (depending on the CB LE version), you could add the folder location where you installled the NI VSTs to the “VST 2 Plug-In Path Settings”. This would be located in the Cubase>Device>VST Plug-In manager menu or, depending on CB version, could be located in the Cubase Studio>Plug-In Manager menu.
You could copy the plug-in .dll or .vst file (or whatever file that is associated with kind of vst you installed) to one of the folders already listed in the VST 2Plug-In Path Settings.
NI VSTs will work with Cubase LE but they need to be setup correctly. Example: if you have a Cubase 9 version that does not recognize 32 bit plugins and that is what you installed… then, it will be an issue. That is why you should always list the pertinent hardware and software specs.
These things could be added to your forum signature.