As mentioned, 락하다 probably means "lock", to set a file or folder protected against an update or delete. So the sentence might mean "(It appears) You better lock this writing" or "Maybe you should lock this writing". But 락하다 is not a commonly used term. For "to lock", 잠그다, 잠금을 걸다, and even 락을 걸다 seem to be better than 락하다.

Or the person would mean '락' as a meaning of 'lock' in English. Namely, the person mixed Korean and English in a sentence.

The sentence itself doesn't make sense indeed. It would better to forget it. Even though I'm Korean, I can't understand the meaning. People often use some silly spoken language without any caution, so I have struggled with trying to understand what people try to mean by their sentence in both speaking or messages.