Numbers 32:38

Nevo, Ba’al Me’on, their names having been changed. Nevo and Ba’al Meon were names of idols. The Emorites would name their cities after their idols, so the sons of Reuven changed their names in favor of other names. This is the meaning of “their names having been changed” — Nevo and Ba’al Me’on were turned aside in favor of a different name.

And Sivmah. They built Sivmah. This is Sevam mentioned above.

and the place of the sepulchre of Mosheh, and (rebuilt) the city of Balak, destroying out of it the idol of Peor, in the house of his high places, and the city whose walls surrounded it, inscribed with the names of his heroes, and Shiran. And after they had built them they called their names after the names of the men who had built them.

Nevo. This could be the Mount of Nevo, where Moshe is buried.

Their names having been changed. These cities had their names changed, and Sivmah as well.

AND NEBO, AND BAAL-MEON — THEIR NAMES BEING CHANGED. “Nebo and Baal-meon were names of idols, and the Amorites used to call their cities by the names of their idols, therefore the children of Reuben changed [the names of these cities and gave them] different names, this being the meaning of the expression their names being changed, which means that Nebo and Baal-meon were changed to other names.” This is Rashi’s language. But the [concluding part of this] verse which says, and they called their names unto the cities which they builded refers to all the cities [mentioned there], and not only to Nebo and Baal-meon [and therefore the phrase their names being changed cannot be understood as Rashi explained it]. Furthermore, what sense would there be in Scripture mentioning the cities [only] by the names of their idols, and saying that the children of Reuben built them and changed their names, without mentioning the good names which they were [now] given! And indeed it is quite usual for Scripture when speaking about [any] captured cities to mention always the new names [given them, as in the following cases]: and they called Leshem, Dan, after the name of Dan their father; and he called them the hamlets of Jair; and he called it Nobach., Verse 42. And likewise wherever the name [of a city] was changed [for any reason] Scripture mentions [the new name as well, as it is said], Now the name of Hebron beforetime was Kiryath-arba; now the name of Debir beforetime was Kiryath-sepher., 15:15.
The most likely explanation seems to me to be that these names [Nebo, Baal-meon, etc.] were the names of the cities when they were in the possession of Moab, and Sihon captured all these cities from the former king of Moab, for thus it is written about Heshbon, Dibon and Medeba, as it is said, We have shot at them; Heshbon is perished, even unto Dibon etc., Verse 30. This also appears to me to be the [meaning of the] words of Jephthah, when he said, While Israel dwelt in Heshbon and its towns, and in Aroer and its towns, and in all the cities that are along by the side of the Arnon, this being the same Aroer [mentioned here in Verse 34] which they took from Sihon. Now when Tiglath-pileser the king of Assyria exiled the Reubenites and the Gadites, the Moabites returned and settled in their lands and cities, for we find in the Book of Jeremiah that when Nebuchadnezzar [king of …

מוסבות שם, “their names having been changed;” originally they had been named by the Ammonites and Moabites. After being conquered by Sichon, their names were changed. When they were conquered by the Israelites their names were changed again to sound Jewish.