You can only reassign the meetings and webinars scheduled from the Webex website.

The current release doesn't support reassigning meetings scheduled in Webex App, Google Add-on and Office365 plugin.
1

Sign in to Control Hub, then go to Services > Meetings.

2

Click Manage Meetings and Webinars.

3

Search for meetings and webinars by host email or meeting number.

4

Select the meetings that you want to reassign.

5

Click the Reassign host link.

6

Enter a host name. Select a host from the list.

7

Click Reassign.