i found these instructions:
How to install a PS2 Flip-Top Cover
Place your console on a table or flat surface
Remove warranty sticker located on the back of the PS2 (Sony warranty is now void)
Turn the console over face-down on the table
Remove the base screw covers & screws based on your version PS2
Set console face-up, and carefully remove top cover, be very careful not to damage the eject ribbon cable, do this stage slowly & carefully
Unscrew the 4 tiny screws on the CD/DVD drive tray cover & lift it off
Remove the white disc from the tray cover itself & insert it in the Flip-Top lid
Unscrew screw from retainer plate & remove Memory Card port covers
Re-attach them to Flip-Top Cover & secure retainer plate with its screw
Remove eject/reset ribbon cable assembly & screw it to the Flip-Top Cover
Slowly slide Flip-Top Cover on console making sure NOT to pinch RESET/EJECT wires
Turn console face-down & replace screw covers & screws based on your model
Job Done!