Numbers 20:25–29 says (NABRE)
Take Aaron and Eleazar his son and bring them up on Mount Hor. Then strip Aaron of his garments and put them on Eleazar, his son; but there Aaron shall be gathered up in death. Moses did as the LORD commanded. When they had climbed Mount Hor in view of the whole community, Moses stripped Aaron of his garments and put them on Eleazar his son. Then Aaron died there on top of the mountain. When Moses and Eleazar came down from the mountain, all the community understood that Aaron had breathed his last; and for thirty days the whole house of Israel mourned Aaron.
The New American Bible has a note to this passage; it states
Mount Hor: not definitively identified, but probably to be sought in the vicinity of Kadesh. According to Dt 10:6, Aaron died at Moserah (cf. "Moseroth" in Nm 33:30–31), which is apparently the name of the region in which Mount Hor is situated.
That's one possibility.
Similarly, the Pulpit Commentary on Deuteronomy 10 states
As Aaron died there, Mosera must have been in the vicinity of Mount Her [sc. Hor].