Rashi on Numbers 32:38/רש"י על במדבר ל״ב:ל״ח

1ואת נבו ואת בעל מעון מוסבת שם AND NEBO AND AND BAAL-MEON, THEIR NAMES BEING CHANGED — Nebo and Baal-Meon were names of idols, and the Ammonites used to call their cities by the names of their gods. The children of Reuben therefore changed their names into other names. This is the meaning of מוסבת שם: Nebo and Baal-Meon were changed to other names.

2ואת שבמה AND SIBMAH — i.e., they built (cf. v. 37) Sibmah also. This is identical with Sebam that is mentioned above (v. 3).