You need to jailbreak your iPhone It only works on iPhone 7 Plus with iOS 11 Tutorial Open Cydia and install Filza. Download the files from this link Open Filza and copy the files you downloaded and past

Disclaimer: Electra is a free jailbreak tool for iOS 11.0 - 11.3.1. It is recommended to futurerestore before running Electra. Although Electra itself should be safe, we are not responsible for any damage

According to www.coolstar.org website, Electra Team are making efforts to deploy the jailbreak for iOS 11.3.1 As you can see it’s a matter of time, probably one day or two to finish the hard work. 😁