How do I enable iMessage on my iMac MacBook Pro.

Hi AmandaGJ,

Welcome to the Apple Community, where some of us do our best to help each other.

Your Apple ID is the account you use to access Apple services,

such as the App Store, Apple Music, iCloud, iMessage, FaceTime and more.

If you forgot your password or Apple ID, go to your Apple ID account page,

select “Forgot Apple ID or password?” then follow the instructions.

Or

If you have changed your Apple ID or password lately you might need to update your sign-in information with any Apple services that you're using. The support page below can help in this situation:

What to do after you change your Apple ID or password:

https://support.apple.com/en-au/HT204071

Or, if all is in order:

Double click the iMessage icon in the dock to open the app.

Sign in with your Apple ID

Set up to send texts using Messages on Mac

https://support.apple.com/en-au/guide/messages/ichte16154fb/12.0/mac/10.14

Change iMessage preferences in Messages on Mac

https://support.apple.com/en-au/guide/messages/icht39422/12.0/mac/10.14

For other details:

Messages User Guide:

Click the Table of contents:

(You might need to choose your OS at the top of some pages)

https://support.apple.com/en-au/guide/messages/welcome/mac

Cheers :)