Possible meanings are 1) the second phrase beginning with "according to" explains the meaning of the first phrase beginning with "according to." Alternate translation: "It was according to the appearance of the vision that I saw when he had come to destroy the city" or 2) the first phrase refers to the vision that Ezekiel had just seen of God's glory. Alternate translation: "The appearance of this vision that I saw was according to the vision that I saw when he had come to destroy the city"
The abstract noun "appearance" can be translated as a verb. Alternate translation: "just like what appeared in the vision" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
"when the God of Israel had come to destroy the city." If the earlier Hebrew reading "when I had come to destroy the city" is used, then "destroy the city" is a synecdoche for "prophesy that the city will be destroyed." Alternate translation: "when I had come to prophesy that the city will be destroyed" or "when I had come to prophesy that the God of Israel will destroy the city" (See: [[rc://en/ta/man/translate/figs-synecdoche]])