Are you talking about the gaskets that are put around the LEDs?
Those are put in place by simply placing it around the led.
Make sure you have the right gasket for your LED.
Meaning : XML2/XHP50 Leds need 5050, XPL need 3535, …

Also try to see if the top diameter is for reflectors 7mm holes or with 9mm hole (diameter in the base) .