If you are getting the alert "this workflow has already been applied to this trip" when attempting to add an Automations Workflow to a trip, you likely have automations on that trip that are also in the workflow you are attempting to apply. Tern will not let you add the same automation to a trip twice.
This is expected behavior so that you don't have multiple automations doing the same thing.
Any automations that are in the workflow that are already on this trip, you will need to delete from the trip. This way when you add the workflow, it won't flag that you are adding some automations twice.
If you confirm that there are no duplicate automations on the trip, and your workflow will still not apply, please reach out to Tern customer support at [email protected]