Here John gives background information that Jesus secures a donkey. He implies that Jesus will ride the donkey into Jerusalem. Alternate translation: "he found a young donkey and sat on it, riding into the city" (See: [[rc://en/ta/man/translate/writing-background]] and [[rc://en/ta/man/translate/figs-explicit]])
You can translate this in an active form. Alternate translation: "as the prophets wrote in the Scripture" (See: [[rc://en/ta/man/translate/figs-activepassive]])