Sign in to TickTick on the web.
Click the "···" button beside a list name. (Note that this button is hidden until the mouse hovers over it. When the mouse is not hovering over it, it shows a number indicating the total tasks contained in the list).
Click "Delete", then confirm it.
Note: Once a list is deleted, all tasks within that list will be removed as well. You may only recover them from Trash.