This is likely due to the "Who is to confirm?" setting in your showing configurations. If you have selected Seller to Confirm and have set SMS as their preferred delivery, the Seller should be receiving a text as soon as the showing is requested. Within that text, they will be able to click the link within the message in order to get to the external dashboard to confirm or deny the showing. If you have selected Auto-Confirm All Showings, contacts will only receive notifications and not have the choice to confirm or deny.
There isn't any Admin action necessary in order for the process to be completed. If/when you see the request for the showing going into the Admin Queue while it awaits Seller action, this is a fail-safe to ensure no follow-ups/reminders need to be sent to the Seller.