If you already have programmed workouts on your calendar, you can use the "Create Variant" option to quickly create brand new, slightly different versions of those workouts.
*Note: If you'd rather fully replace the existing workout, instead of creating a separate variant, see How do I make edits to programmed track events?
To create a new variant of a programmed workout, follow the steps below...
Step 1
Find a programmed workout from any of the calendar views (Month, Week, Day), click on the track event, and select the "Create Variant" option from the pop-up menu that appears.
Step 2
A copy of the existing workout is created. Edit the workout via the various actions available to you (Edit, Copy, Delete, Add Movement, Add Complex, Add Rest, etc). 
*Note: if you want to add this variant to a different track and/or to a different day, make sure you update those fields, too. 
Step 3
When finished, click the "Plan Workout" button.
If successfully created, you'll see the toast notification appear at the bottom of the build modal. It will read...
"This workout now appears on your programming calendar."
Your calendar should now display BOTH the original workout and the new "variant" you just created.