Start MAMP
The MySQL server must be running to change the password, open and start MAMP now. keep it running until the end of this.

Mac Terminal
With the MySQL server running, open the terminal (located in '/Applications/Utilities') enter or copy/paste the following:

/Applications/MAMP/Library/bin/mysqladmin -u root -p password
You'll be prompted for a password. Enter the current password for the root user. If you changed it in phpMyAdmin, use that password.

Mosty password is blank so just press Enter and Enter Your New Password.

$ /Applications/MAMP/Library/bin/mysqladmin -u root -p password
Enter password:

$ /Applications/MAMP/Library/bin/mysqladmin -u root -p password
Enter password: 
New password: 
Confirm new password:
Now You Have to make changes in some file:

You need to replace all occurrences of the old root password with the new one you just created. To keep it easy here is a list of the files, you can open them in your favorite text editor and search for 'root', changing '-proot' to '-p NewPassword', replacing 'NewPassword' with your own.

/Applications/MAMP/bin/phpMyAdmin/config.inc.php
/Applications/MAMP/bin/checkMysql.sh
/Applications/MAMP/bin/quickCheckMysqlUpgrade.sh
/Applications/MAMP/bin/repairMysql.sh
/Applications/MAMP/bin/stopMysql.sh
/Applications/MAMP/bin/upgradeMysql.sh

Stop and restart MAMP

I hope that works/make sense because this works for me.