Here the typesetter for the 1852 LDS edition accidentally replaced the preposition by with to. The resulting text, the reading in the first printing of that edition, has to followed by into, which won’t work geographically: “the narrow pass which led to the sea into the land northward”. The second printing of the 1852 edition restored the original preposition by, probably by reference to the 1840 edition. The critical text will, of course, maintain the original by.
Summary: Maintain the preposition by in Alma 50:34: “which led by the sea into the land northward”.