John Gill Commentary Deuteronomy 2:1

"Then we turned, and took our journey into the wilderness by the way to the Red Sea, as Jehovah spake unto me; and we compassed mount Seir many days." — Deuteronomy 2:1 (ASV)

Then we turned
From Kadesh, where they had been many days, and so also their backs on the land of Canaan, on the borders of which they had been:

and took our journey into the wilderness, by the way of the Red sea, as
the Lord spoke to me ;
(Deuteronomy 1:40)

and we compassed Mount Seir many days ;
Many think by Mount Seir is meant the whole mountainous country of Edom, about which they travelled to and fro in the wilderness that lay near it for the space of thirty eight years, which they suppose are meant by many days.

But I rather think they came to this mount towards the close of the thirty eight years, before they came to Kadesh, from where they sent messengers to Edom, which they went round about for several days.