To create a new trip from an old trip in Tern, use the trip duplication feature:
Log into Tern and select the trip you want to duplicate.
Click on the ellipses (three dots) next to the 'share itinerary' button.
Select 'Duplicate Trip'.
Choose which data to carry over, such as Prices, Commissions, and Payment Groups.
Click on 'Duplicate Trip' and rename the new trip.