To reset your login manager password, you need to use a tool called "passwd". "Passwd" is a basic tool used to change or reset user passwords.
First, open up a terminal window and type the command "sudo passwd". You will then be prompted to enter your current password (if necessary) and then to enter the new password twice. Once you have entered the new password twice, it will be set as your new login manager password.
It's important to note that if you have forgotten your current password and you are unable to log in, you will need to use a different method to reset your password, such as booting into single user mode or using a recovery disk.