If you used the application to lock you device, type "forgot password" or "?" as password and enter the security answer. If the device wasn't configured with this kind of recovery method, type your email address in the provided field and wait to receive the reset code. Use this code to unlock the phone. If this doesn't work, I recommend you contact the developers using
firstname.lastname@example.org email address. If they can't help you, you will need to factory reset the device. You can find the necessary instructions in the user guide of your mobile. Basically, you need to power off the phone and to press simultaneously Volume Up + Power buttons. Select Wipe data/Factory reset from the recovery menu and follow the on-screen instructions.