Did you add the VST installation path of EZ drummer to your locations configuration in Studio One and did you rescan your plugins after adding the new location to your VST configurations?
If your answer is no, you should review this guide:
https://support.presonus.com/hc/en-us/articles/210043983-Studio-One-How-do-I-add-a-3rd-party-VST-to-Studio-One-