question about triggers and effects

[samedi]

Hello i have a problem on the gem editor, for example i want a trigger that says "if this unit is to die then this squad should come to replace them, i put the reinforcement squad a tag and "hidden" but i dont know the condition i need to put in that says if this unit is to die then this squad move to replace them and if that squad is to die an exact replicate of that squad should replace them please help me