Since this happens after Joash takes the bow and arrows, he may have had a servant open the window. AT: "So a servant opened it" (See: [[rc://en/ta/man/translate/figs-explicit]])
The relationship between the arrow and victory can be stated explicitly. AT: "This arrow is a sign from Yahweh that he will give you victory over Aram" or "This arrow symbolizes the victory Yahweh will give you over Aram" (See: [[rc://en/ta/man/translate/figs-explicit]])