Get a good bulb...an OEM replacement may be the way to go since the LEDs do not seem to work well.
--Is there power at the light socket? If so, replace bulb and you should be good.
---If no power at the light socket...is there power coming into the switch (which may be integrated with the socket)?
----If there is power coming from the car to the switch/socket, none at the socket...replace the switch/socket.
----If no power to the switch/socket...check the fuse (you may wish to check the fuse earlier in this process).
----If the fuse is known good, but there is no power at the fuse block, internet search for a procedure to reset the courtesy/trunk lights...it may be a computer time out.