I was wondering that if I equip the headband of intelligence to my steel defender it would technically get a 19 intelligence. How would this work? would it become self-aware and follow a series of complex instructions or use their own abilities to try to help. I imagine with a 19 in intelligence I would think if I was to go down it would be able to try to revive myself or find a way to protect such as dragging away from combat. Any suggestions would be amazing or examples I could suggest to my dm. It could also be a way for me to create 'protocols' in which it can use in combat or out of combat and also use items within reason such as administrating a potion or stabilising a creature. 

Not self aware.  It's intelligence already exceeds that of the stupidest human. 

Intelligence is a pre=requisite for self awareness, not the definition of it.

But he should be able to understand complex commands, such as "If I go down, heal me".

At this level of intelligence, you could probably give it one order, such as "keep me alive", and it would improvise and develop the best strategy to do so on the spot. I don't think it would be truly self aware, just highly advanced.