Unzip and move AltStore to your Applications folder. Launch the AltStore application.
Click on the AltStore icon in the Menu Bar, and then click on the Install Mail Plug-in option.
Open the Mail app, and click on Mail → Preferences in the menu bar.
Open the General tab in mail preferences, click Manage Plug-ins, check AltPlugin, and apply and restart Mail.
Connect your iOS device via USB.
Click AltStore in the menu bar, then go to Install AltStore → (Your iOS Device)
Login with your Apple ID when prompted and click install.
On your iOS device, open Settings → General → Device Management and tap on your Apple ID.
Tap the "Open in AltStore" button located above.
AltStore will now install the app. Wait until it finishes.
Open unc0ver and jailbreak!