Through prayer. If you would like to, you can always buy a candle dedicated to St. Michael but praying will do just as well.
"O glorious prince St. Michael,
chief and commander of the heavenly hosts,
guardian of souls, vanquisher of rebel spirits,
servant in the house of the Divine King
and our admirable conductor,
you who shine with excellence
and superhuman virtue deliver us from all evil
,who turn to you with confidence
and enable us by your gracious protection
to serve God more and more faithfully every day."
You can always change the one stated above or make up your own, either will work just as well.