Creating a fixed segment of users on Adobe Analytics

Hello,
I want to create a segment of all the customers who upgraded their devices on April.
More formally, the visitor has the "upgrade_successful" HIT page during April. 
My objective then is to look on that group of users, and examine how they behave before/after the upgrade (it can be at any month!)

I want all <VISITORS>:

1. Who had my app domain HIT

AND

1. April AND Upgrade_ successful HIT

Thank you!