Based on instructions from here: https://dev.mysql.com/doc/refman/5.7/en/osx-installation.html
Following step 2.4.2 download the .dmg image from here
On the download screen, you can skip login by clicking this at the bottom of the page:
No thanks, just start my download.
Make sure you write down the temporary password it creates in Step 7, you will need it soon.
Step 2.4.3 Installing a MySQL Launch Daemon
Follow the steps explaining how to use System Preferences.
At this step, do no select the box for automatically starting up the server. Otherwise you will have MySQL running every time you use your computer.
Update your bash profile
echo 'export PATH=/usr/local/mysql/bin:$PATH' >> ~/.bash_profile
exit the terminal session and start a new one.
Login to mysql as the root user.
mysql -h localhost -u root -p
Use the password you wrote down earlier
You will see a screen like this
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 90
Server version: 5.7.21
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
Using the mysql> propmpt, reset the root password:
ALTER USER 'root'@'localhost' IDENTIFIED BY '<your new password>';