If one of your sales channels becomes disconnected from Sellbrite, you can try to reconnect it by simply clicking the 'Reconnect' button found in the Channel Settings page.
You can find this page by navigating to Settings > Sales Channel Integrations and select the channel that has been disconnected.
If that does not work, you may need to take some additional steps to get your account reconnected. To learn more about reconnecting a specific sales channel, check out the links below: