Some of our Skype for Business Online users need additional time to upgrade their Attendant Console for Skype for Business or other Skype for Business extensions like Attendant Console, Public Announcement System, Door Bell, Elevator Phone, Virtual Receptionist or other ISV solution to Microsoft Teams. If you need additional time to upgrade to Microsoft Teams you request an extension. Below we outline how to extend your usage of Skype for Business Online beyond July 31, 2021. (Skype for Business Server will be support well beyond 2021, so is not in focus here.)
The first step is to watch your Teams Admin Center (TAC) for a Microsoft Teams upgrade notice.

When you receive it click “Request extension”. Next you will explain your reason for wanting an extension.

You will now be notified that your Skype for Business Online extension request has been received.

After a few days you will a notification in Teams Admin Center (TAC) about your extension. (In our case it was 2 days). It should like something like the below.

We suggest that you work towards upgrading to Microsoft Teams as soon as possible. If you need help migrating to a Microsoft Teams Attendant Console, you can monitor our progress here.