Office Pro Plus 2019
I have the "Key number" I'm not sure where to enter it on my MacBook Air.
Question marked as
I assume you have a local .dmg file and are planning on using it to install Office 2019. You enter the key when it's called for during installation.
I think that also works for the digital installation too. But at any rate, the suite will tell you when it's needed. However, most versions of Office 2019 don’t include a product key and you only need to sign in with the account already linked to your Office license.
In my opinion, Microsoft doesn't help any by changing how this done with new Office versions.