Here "himself" emphasizes that the same person—Makir—was the firstborn of Manasseh and was also the father of Gilead. Alternate translation: "firstborn; he was also" (See: [[rc://en/ta/man/translate/figs-rpronouns]])
This can be stated in active form. Alternate translation: "Joshua assigned the land of Gilead and Bashan to Makir's descendants" (See: [[rc://en/ta/man/translate/figs-activepassive]])