Note: if you have not done so, please read the introduction to Upgrading a PS3 Hard Drive before performing these steps.
Now you simply slide the carriage. back into its original location, the carriage. will help to guide the drive to the connectors. Gently move the hard drive into the slot and when you reach the end use a firm press to ensure the connections are made properly. Don't go overboard though, pressing too hard may damage other components of the PS3.
With the new hard drive securely in place, simply re-secure the one screw to the carriage and place the HDD cover plate back on the side of the PS3. Move on to the next step.