Had this annoying issue too. If you screw up a signal job, sometimes you are gonna have to re-load a old save file.
Reverse might help.
Putting one train on a new line may help to get it to go backwards.
GoTo Depot probably wont work if both trains are dead locked.
Or reload a old save file.
Be nice for a “delete” button or able to bulldoze a train. Maybe for a high price or something, but things do happen. I’ve also had this happen more then few times it also makes it ALT+F4 rage worthy. But I just reload a save.