Mac Computers

Go to  - Systems Preferences -

Click on Input Sources 

Click on the + 

Scroll down until you see Maori  Click on it and then click Add

Check that Show input menu in menu bar is ticked

Look at the top of your menu bar, you will see a flag , click on the Flag and you will see all the Keyboards you have installed

Click on the Maori Keyboard, hold down the Tilda key ~ on the Keyboard and press the aeio or u keys to  get ā ē ī ō ū