The easiest way to do this is to meditate and take note of any sounds or phrases of power that are being transmitted into your mind from the outside. Depending on what you are trying to accomplish it comes out differently, but it will most likely resemble existing light language or mantras of other faiths.

When meditating with the intention of this, your mind is able to connect to these energies and translate them into mantras. Write them down to avoid losing them and return to the later. The easiest ones to channel are the ones connected to deities you work with on a regular basis. Other chants like mantras of enlightenment are trickier to find because they come from within. Your ancestors may also have some things for you to chant that are tailored to you specifically which will be more effective than the things you just find online.