Your boot button has fallen out because the small rubber o ring which holds the button componant in place has worn out and broken causing the button to be ejected. The picture shows a complete o ring on the left and a perished o ring on the right. My soloution to this was to produce a cost effective fix fo rthis common problem. I produced a custom machined metal clip which can be crimped into place and will not wear out. This can be purchased at my online shop:
If you have also lost your button these can also be purchased here as well as the spring componant and colour coded button options. The following tutorial shows how to repair your lock using these componants. This repair is suitable for Renault Scenic models from 1999-2003 and all Renault Megane models of the same year.
Open the boot and using the T-20 Torx screwdriver unscrew the four screws, whichhold the interior boot trim in place (some models have an additional two screws near the wiper motor). Unhook the parcel shelf bungees from the trim. To remove the trim, pull firmly all around the edges, you will heara snapping sound, this is just the clips thathold it in place.