How to reset a forgotten password for any user under Linux Mint 21 even where you don't know the system administrators password or users password for which you would like to change.
1. Turn your computer on
2. Wait for the Linux Mint splash screen to appear and then hold the CTRL and ALT keys down simultaneously and while doing this tap the delete key; this will cause the system to restart and present you with a GNU GRUB boot menu
3. Once you see the boot menu select Advanced options for Linux Mint using the arrow and enter keys
4. Select from the shown menu one of the entries that has (recovery) in the name
5. You will see a Recovery Menu appear, here you need to select the root option from the list using the arrow keys on the keyboard and the enter key
6. Hit the enter key for maintenance
7. Enter the command passwd [user_name] and hit the enter key.. this will allow you to change the password for the user
Example: passwd think
8. Enter a new password, you won't see any letters appear on the screen, this is normal, hit enter when finished entering a new password
9. Retype the new password you wish to set for the user and hit enter
10. If you sett a message that says passwd: password updated successfully you've successfully updated the password for the user and restart the machine
11. Hold down these three keys to reboot:
CTRL+ALT+DEL
12. Try logging in as user whose password you reset