you don't have an integrated headset. they didn't exist in the 80s and they need dedicated headtubes (can't be retrofitted) and they only work with 1 1/8 threaded set-ups.
you need to take tis bike into a store and have the guy fix it and explain it to you at the same time. better a proper clarification and then you cn do it yourself in the future than to tyro-diy and fuxor it up, imo