In Manager, navigate to the folder where the target Task resides.
Select the target Task, then on the Assets Toolbar click Enable.
Since Triggered Tasks run as single instances of a Pipeline execution, you can use the Enable/Disable functionality to allow the Task to be Triggered. However, Enabling a Task does not actually Trigger it.
In the Assets View:
In Manager, navigate to the folder where the target Task resides.
Select the target Task, then on the Assets Toolbar click Enable.