Open the config.yml file of the DiscordSRV plugin. Add your channel id to the channels array.
The identifier inside the array must be "staffplusplus-<channelname>" . By default staff++ only has one staffchat channel, name "staffchat". So in this case I will configure "staffplusplus-staffchat".
If you have for example another channel configured in staff++ called "adminchat", you can add another channel in the discordsrv config called "staffplusplus-adminchat".