The Trio 8300 follows the same Multiple Key Combinations as the VVX phones shown >here<.
You can also follow these instructions >here< that show how you do this via the Web UI or Phone Menus.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's