The TCDRP is a simple wrapper that allows other mods to access the Discord Rich Presence API through a simple API.
On your mod's initialization (Awake function):
TCDRP.API.InitRPC(clientId);Setting an activity
TCDRP.API.SetActivity(Plugin.clientId, state:"Choosing a save");Note: You can set variables as mentioned in Discord documentation.
If you need more help, read through the API implementation in TCDRP/API.cs or read through the TestTCMod implementation.