Here the throne represents ruling. Establishing the throne of Solomon's kingdom represents causing Solomon to have descendants who will rule over Israel. Alternate translation: "I will make descendants of yours rule over your kingdom" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This can be stated positively. Alternate translation: "One of your descendants will always be ruler in Israel" or "Descendants of yours will always rule in Israel"