Go to Marketing> Emails > Email Campaigns>Create Campaign or Edit an existing campaign.
Please Note: Content AI is available in Email Templates as well as and Email Campaigns.
For Email Templates, head to Marketing>Emails>Templates>New, or Edit an existing template.
Drag and drop a Button Element into the Email body, then click on Content AI.
Enter Content Description to describe what kind of text you want to generate; choose the Number of Variations you wish to create, and then click on Generate. It will then ask you which of the Variations you want to use. Click on Copy next to the one you want to use, and then click Continue.