with a chant or anointing it with oil. personally with luck i use cinnamon, but i use cinnamon in almost everything, so try to find an herb/spice you're connected to that have good luck qualities.
you should probably hold off since it's the waning moon and this phase works with taking things away. [maybe a take away bad luck spell could work] anyway, what i've done in the past is take a charm, start by leaving it in salt water in the window for a few days [if you want it in sun or moon water take it out of the sun/moon light. meaning if you want it to be solar water, take it out of the window before the moon rises] this should purify it from all energies it's probably picked up. then anoint it with some type of luck oil, and pass it through some incense [cinnamon] while saying some type of luck chant. be sure you charge it with energy while doing the chant. green candles are also used for luck, maybe burn one while making the charm. sorry i'm being vague, but you should personalize it since you're the one who's using it.