You haven't given any info on what you've tried and what version of Studio One, so I can only guess. I'm assuming you have Artist or Pro, since Prime doesn't allow third party VSTs. 32bit plugins don't work on 64bit Studio One. From these assumptions I'd guess you might need to set up their locations. Click Studio One > Options > Locations > VST Plugin Ins > Add and add the location of your VSTs. Could be in a few places like "C:\Program Files\VSTPlugins", "C:\Program Files\Steinberg\Vstplugins", "C:\Program Files\Common Files\VST3", or you might have to find them yourself.