Install actual version during beta/alpha test (Android)

I would like someone else to test a migration process of my app. My App actually has version 10. My App published to Alpha has version 11.

I added the tester to the list of Alpha testers and he can install the new version 11 successfully.

Now the question : How can my tester install the older version 10, even the tester is in the list of alpha testers, without removing him from the Alpha-Testers list ? Are there 2 different links, where we can install both the newer and older version without manipulating the list of testers ?