Apple Macintosh 6500 - Manual (Page 209)

To install a communication card, follow these steps:
1 Remove the plastic access cover from the vertical plate.
Save the access cover—if you ever remove the communication card from your
computer, you’ll need to cover the open port again.
2 Remove the communication card from its static-proof bag.
Hold the card by its upper edges to avoid touching its connectors.
Push the two plastic tabs apart and pull off the
metal retainer so the access cover can come off.
Metal retainer
209 Installing Expansion Cards or Additional Memory