You can’t kill them really, you end up making it so they are “dead to you” and don’t exist in your corner of the universe.
But try this:
Lesh ta pak een lafa tu son - To Neutralise and Repel Negative or Harmful Energies
When using this mantra against psychic attack, chant out loud forcefully if possible. If using it against a toxic environment or person, chant mentally if you cannot do so vocally.