It is not possible to edit two of your apps in different tabs at the same time. If you try to have the content open for two different events, edits will only be saved for the event that was most recently opened.
Although you can’t edit apps simultaneously within tabs of the same browser window, you can still do this if you open a private browsing window in your current internet browser. This way, you can edit one of your event apps in the main browser window, and another one in the private window.
If you have another internet browser on your computer, you can also edit another app in that different browser as well without affecting the other apps you have open.