ब्रह्मैवाहं न संसारी मुक्तोऽहमिति भावयेत् ।अशक्नुवन्भावयितुं वाक्यमेतत्सदाऽभ्यसेत् ॥ १८ ॥
In plain words
"I am Brahman itself, not someone caught in saṃsāra. I am free." Dwell on that. And if the dwelling won't come, then repeat the sentence — always, keep repeating it.
Close to the Sanskrit
"I am Brahman alone, not one who wanders through saṃsāra; I am free" — thus one should contemplate. Being unable to contemplate, one should always practise this sentence.