Yahweh is implying that they will know that he is the one true God who has supreme authority and power. See how you translated as similar phrase in [Ezekiel 6:7](../06/07.md). Alternate translation: "they will understand that I am Yahweh, the one true God" or "they will realize that I, Yahweh, have supreme power and authority" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here "set fire in Egypt" represents sending an army to attack Egypt and set fires. Alternate translation: "when I send an army to burn Egypt with fire" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This can be stated in active form. Alternate translation: "I destroy all of the allies of Egypt" or "when armies destroy all of those who help Egypt" (See: [[rc://en/ta/man/translate/figs-activepassive]])