Studio One does not natively support any bit-bridging technology to make 32-bit plugins work in the 64-bit version of Studio One. You have a few options:
1. Buy something like J-Bridge to wrap your 32-bit plugins to 64-bit
2. Use the 64-bit versions of said plugins if available, or
3. If no 64-bit versions available, consider transitioning away from those old plugins. You may not like this option, but if a plugin hasn't been updated yet to support 64-bit VST, then what are the odds that same plugin will work in the next iteration of your OS or host? What about the next 3 iterations? The honest truth is software that isn't actively being updated just isn't going to be guaranteed to work down the road, so if you want to avoid recall issues, the sooner you stop using abandonedware, the better off you'll be.