A letter from the prophet Elijah came to Jehoram

"Jehoram received a letter from the prophet Elijah" or "The prophet Elijah sent a letter to Jehoram"

walked in the ways

This is an idiom that means he followed their example. See how you translated this in 2 Chronicles 20:32. AT: "followed the example" (See: rc://en/ta/man/translate/figs-idiom)