I think you fundamentally misunderstand how technology works. Human science is built on the shoulders of past discoveries, an aggregation of thousands of years of knowledge.
It's possible for things to be preserved- there are probably some blueprints here or there. But even that is not enough, without the theoretical background and the practical skill to construct what they need to construct.
Hell, look at this:
Do you know how this circuit diagram works? Did you even
know this was a circuit diagram? Do you know what it's for? It's for a computer motherboard.
Now imagine your level of confusion, but now add that
1. you don't know what a circuit diagram is
2. you don't what a computer is
3. you don't know what electricity is
And you begin to realize the problems involved.