Since there is no model of the device specified in the question, I can provide a general way to unlock the device. Charge the phone/device to 85 % or more and then turn it off. Remove the battery and plug it back. Press the following button combinations until you access the Android logo, therefore Recovery mode:
- Volume UP + Volume Down + Power button
- Volume Up + Power button
- Volume Down + POwer Button
- Volume Up + Home + Power
One of these combinations will take you directly to the Recovery Mode. Once you are in the Recovery Mode, select Wipe Data/Factory reset. This will wipe all the settings and applications, including the phone/device lock.
After this procedure, the phone/device will be completely free to access. Initial configuration needs to be completed before usage.