Navigate to Works on the side tab bar

Select WTMP on the top tab bar

Select the WTMP to add a plan to

Scroll down in the overview of the works to the Required Plans section

+New

Select Works Revision from drop-down

Select Plan Type from the drop-down. Select the + to create a new Plan type

Create

Choose a plan from Attach Plan drop-down or select the + button to create a new plan to attach

Save