This is not a process to be accomplished by a general technician.
It requires a "clean room" and a lot of experience and training.
Most companies that do such work hold their processes as "trade secrets".
With that being said, here's a wiki article
about swapping out platters in a hard drive.
I don't recommend you even attempt this process.
The only easy day was yesterday.
...some do, some don't; some will, some won't (WR)