This popup is available from the Availability Confirmation page.

On the left of this page you will find various filters  to help refine options based on your requirements.

You can filter by Shift or by Roles and also filter by Keyword or History. You can display  employees that are already assigned, expired and pending compliance

Each employee has multiple icons assigned to them (bottom right) describing the app activity, if they worked for this organisation earlier, etc.
Other examples include viewing blacklisted or maybe fully vaccinated employees. There are also 2 checkboxes for selecting employees that have Mobile availability and are within the working radius range.
You can select the employee by clicking on them (they will be highlighted in green). When saving, you can decide whether you want to send these employees a message to the App which will display a notification straight away. You can enter text for the message, the employee will also see the shift details.

Just check the Message box and the employees will see the notification straight away in the app once you have saved the page.