The purpose of session tokens is for user authentication, not roles and permissions. More information about session tokens can be found here.
You can, however, use the user metadata to store a role. You can then enforce your own permissions at the client UI level (won't be restricted by the SDK or SendBird itself). Alternatively, you can make a call to your application's own server, authorize the request based on the user's role, and then make a platform API request if the user is authorized to perform that action. More information about user metadata can be found here.
Additionally, some channel activities can be managed by assigning a user as a channel operator. This allows the user to perform channel moderation actions such as banning or muting other channel members. More information on that can be found here.