When my younger brother was using my Samsung galaxy s7 edge, he chang

Once the phone has a screen lock enabled and you or the other person does not know / remember the code to unlock it, the easiest way is to perform a Wipe data / factory reset in the recovery mode menu.

To do this you will need to :

1. Turn off the phone
2. Hold Volume up + Power + Home, release power once you see the Samsung text displayed and keep holding the other keys until you get into the recovery mode menu. Initially it will display a blue screen with Android logo saying updating system software or something like that, let that go and it will eventually boot into the recovery menu.
3. Use volume up and down keys to navigate the menu
4. Once you have selected Wipe Data / Factory reset press power button to confirm doing it.
5. Note that this will wipe all data on the phone, if you need to backup data then sorry but you are out of luck in this case.
6. After wipe data / factory reset is done reboot the phone and wait for the phone to fully boot up which may take some time.