John Gill Commentary Numbers 32:38

"and Nebo, and Baal-meon, (their names being changed,) and Sibmah: and they gave other names unto the cities which they builded." — Numbers 32:38 (ASV)

And Nebo, and Baalmeon, (their names being changed,)
&c.] For Nebo was the name of an idol, after which perhaps the city was called: Baalmeon signifies "Baal's habitation", and where it is highly probable was a temple of his; and the children of Reuben, not liking to retain such idolatrous names, gave them others, but what they were it is not said; and certain it is, that when these places came into the hands of the Moabites, their ancient names were restored to them, as appears from (Isaiah 15:2) (Jeremiah 48:23)

and Shibmah ;
the same with Shebam, (Numbers 32:3) , and gave other names unto the cities which they built; but they are neither known, nor did they always continue, as has been observed.