Jeremiah 52

Nephi asks those in the Americas -

"...will you dispute that Jerusalem was destroyed? Will ye say that the sons of Zedekiah were not slain, all except it were Mulek? Yea, and do ye not behold that the seed of Zedekiah are with us, and they were driven out of the land of Jerusalem?..."  (Helaman 8:21)

We read in Jeremiah that -

"...the king of Babylon slew the sons of Zedekiah before his eyes: he slew also all the princes of Judah in Riblah.
11 Then he put out the eyes of Zedekiah; and the king of Babylon bound him in chains, and carried him to Babylon, and put him in prison till the day of his death."  (Jeremiah 52:10–11)

In my mind, it is obvious that Mulek either saw or a least knew his brothers were slain.  Which would suggest to me that he somehow escaped after or during the time his brothers were slain.  How that happened and how he was lead to the promised land will have to be revealed at some future day.