In te reo Māori, macrons are known as tohutō: tohu meaning a sign or a symbol, tō meaning to pull or heave: they are symbols that stretch. You can embed tohutō into your keyboard and your practice.
First install the Te Reo Māori language pack. Click the language in your toolbar (probably English in the bottom-right corner, next to the date and time):
If the Te Reo Māori language pack is already installed, you will have an “MRI” keyboard option. Select that and skip to the next step.
If Te Reo Māori isn’t installed, select Language preferences > Add a preferred language > Te Reo Māori > Next. In the next screen, “Install language pack” must be ticked; all other choices are optional. Then select Install. Once installed, you can click on the ENG in your toolbar (same as the first step), then select the “MRI” keyboard option.
With the Māori keyboard option selected (“MRI” will show in your toolbar) you can use the backtick button for tohutō/macrons (the little-used button in the top left-hand corner of your keyboard, sharing a key with the “~” symbol.).
Press backtick and any vowel for the tohutō/macron version of that vowel. e.g. press backtick+a for ā. You can either hold down backtick and the vowel key at the same time, or press backtick first, release, then press the vowel key. If you want a capital tohutō/macron vowel, e.g. Ō, you need to press backtick first, then shift, then the vowel. If you press shift first, you will get a ~ instead. If you do need a backtick for some reason, press backtick twice.
You can toggle between English and Te Reo Māori keyboards at any time from the toolbar.