Whether you updated your iOS device to iOS 9.3.4 or iOS 9.3.5 deliberately or by accident, you can no longer downgrade back to iOS 9.3.3. Apple has now closed the signing door and that means you will be stuck without the ability to jailbreak until a new one is released. As that is not likely to be until after iOS 10 download [ext link] is released now, you could be in for some wait. Most jailbreakers will be lamenting the loss of TinyUmbrella [ext link], a highly useful tool that helped you to save your SHSH blobs whenever you updated your firmware to a new one. Saving these blobs meant that, should you want to, you could downgrade your firmware back to one that could be jailbroken but, at this moment in time, we have no way of doing it.
Image : Prometheus Can Downgrade iOS 9.3.5 to iOS 9.3.2
There could be a light at the end of the tunnel though with a new tool that is apparently in development. It’s called Prometheus and a video showing it working was uploaded by the developer, @tihmstar [twitter]. The video clearly shows an iPhone 5S having successfully done Downgrade iOS 9.3.5 to iOS 9.3.2 [ext link] with Prometheus, although the tool is only partially working at this stage.
Video : Downgrade iOS 9.3.5 to iOS 9.3.2
Because it is still in the development stage, we don’t have any more information to offer you. We do know that, as @tihmstar has mentioned, it will require the use of APTickets, along with a few other conditions that haven’t yet been worked out. For those who don’t know, APtickets are a newer format of the SHSH blob and are used in the same way – to downgrade to an older firmware version – provided you save them every time you update your firmware.
We also don’t have any idea is to when Prometheus might be released, if ever. The developer says that there won’t be any point in releasing right now, partly because it is still in development and partly because it is a highly complicated tool that no one would know how to use. That said, if it ever is completed and released to the public, it will be the only tool of its kind in existence that allows the 64-bit devices to downgrade.
Image : Prometheus Downgrade Tool Concept
So, to reiterate, if you have a jailbreak on your iOS device and you don’t want to lose it, don’t upgrade to iOS 9.3.4 or iOS 9.3.5. You will not be able to downgrade and you will have to wait for the next jailbreak and that could be some time away.