Cant log in

Hello,

Try this

Reset using the Reset Password assistant (FileVault must be on)

If File Vault  is turned on, you might be able to reset your password using the Reset Password assistant:

1. Wait up to a minute at the login screen, until you see a message saying that you can use the Power Button on your Mac to shut down and start up again in Recovery OS. If you don't see this message, FileVault isn't on.
2. Press and hold the power button until your Mac turns off.
3. Press the power button again to turn on your Mac.
4. When the Reset Password window appears, follow the onscreen instructions to create a new password.
5. If you need to connect to Wi-Fi, move your pointer to the top of the screen and use the Wi-Fi menu to connect. To exit without resetting your password, choose Apple menu > Restart.
6. When done, click Restart.
7. If you were able to reset your password with the Reset Password assistant, log in to your account using your new password.

https://support.apple.com/en-us/HT202860

Hope this helps!

Hello,

You may need to completely restore your device by going on to recovery mode.

this will result in data loss

1. Turn on your Mac and immediately press and hold these two keys: Command (⌘) and R. 
2. Release the keys when you see an Apple logo, spinning globe.
3. You might be prompted to enter a password, such as a Firmware Password or the password of a user who is an administrator of this Mac. Enter the requested password to continue.
4. Startup is complete when you see the utilities window:

1. After starting up from macOS Recovery, select a utility, then click Continue:

• • Restore From Time Machine Backup: Restore your Mac from a Time Machine backup.
  • Reinstall macOS: Download and reinstall the Mac operating system.
  • Get Help Online: Use Safari to browse the web and find help for your Mac. Links to Apple's support website are included. Browser plug-ins and extensions are disabled.
• Disk Utility: Use Disk Utility to repair your disk or erase your disk or other storage device.
• 
  
  • Additional utilities are available from the Utilities menu in the menu bar: Startup Security Utility (or Firmware Password Utility), Network Utility, and Terminal. 

1. To quit macOS Recovery, choose Restart or Shut Down from the Apple menu . If you want to choose a different startup disk before quitting, choose Startup Disk from the Apple menu.

The links will direct you to further apple assistance if you have any other issues