Search here in the forums, you will find a link to request it via testflight.
Then you have to wait to be approved by @proclaim who is currently on vacation.
Then you might have to downgrade FLUX Studio several versions below the current version since the app is not working anymore. (No guarantee that will work either.)
In other words, wait a few days until @proclaim gets back, and then we can both make some more noise in this thread about how those that want the app can get it, and how we can get the app working again since it's been broken for a while now.