Is the module the same thing as the ECU and how do I change it

How do I change the module for peugeot 207 sportium 61 plate, UK? Was looked at by AA due to power steering failure. He ran diagnostics and came up with some fault coodes and also reset by taking fuse out and putting back in which caused the power steering to return for a minute then go again. He said it was the module (which I believe is the same thing as the ECU) what do I do? Who do I need to contact to get this repaired in the cheapest possible way but correctly