Swapping Operating System Chip

I took apart my computer for the first time yesterday to clean it and I took out the hard drive to dust the compartment and some of the gold plug prongs on the back of the os were bent. So I had to get a new one but the tech worker said I'd have to buy a new os unless the green little chip is the same shape on the back of both hard drives, and that I'd just have to swap them. They are thankfully, but then he said he couldn't talk anymore about it bc they can't work on things like that. So I was wanting to make sure I'm doing the right thing here. Any help is suuper appreciated !