First, don’t panic! This is usually a simple matter so long as you have physical access to the console.
Simply follow the steps below to boot the system bypassing login, and then set a new password:
Step 1. Reboot the system. Make sure your physically present.
Step 2. When the Grub menu comes up, press “e” to edit the menu selections.
Step 3. Select the kernel you would usually boot and press “e” to edit the settings.